1. Punishment expiates sins
The Prophet added: "Whoever among you fulfills his pledge will be rewarded by Allah. And whoever indulges in any one of them (except the ascription of partners to Allah) and gets the punishment in this world, that punishment will be an expiation for that sin. And if one indulges in any of them, and Allah conceals his sin, it is up to Him to forgive or punish him (in the Hereafter)." - Volume 1, Book 2, Number 17: Narrated 'Ubada bin As-Samit
Abu Hurairah also reports that Allah's Messenger, peace be upon him, said: "For every misfortune, illness, anxiety, grief, or hurt that afflicts a Muslim -even the hurt caused by the pricking of a thorn - Allah removes some of his sins." Ibn Mas'ud said: "I visited the Messenger of Allah, peace be upon him, while he had a fever. I exclaimed: 'O Messenger of Allah! You have a high fever! ' He said: 'My fever is as much as two among you [might have]. ' I asked: 'Is it because you have a double reward?' He replied: 'Yes, that is right. No Muslim is afflicted with any hurt, even if it is no more than the pricking of a thorn, but Allah wipes off his sins because of it and his sins fall away from him as leaves fall from a tree'."
A woman of Juhaina came to the Prophet (s.a.w) when she was pregnant owing to fornication, and said, "O Allah's Prophet, I have committed something for which a prescribed punishment is due, so execute it on me." Allah's Messenger (s.a.w) called her guardian and said, "Treat her well and when she delivers bring her to me." and he did so. Then He gave the command regarding her and her clothes were tied around her body and then He gave command regarding her and she was stoned to death. He then prayed over her. Umar thereupon said, "Do you pray over her, O Allah's Prophet, yet she has committed fornication?" He replied, "She has repented to such an extent that if it were divided among seventy people of al-Madina, it would be enough for them all. Have you found any repentance better than she having sacrificed herself for the sake of Allah the Most High?" [Related by Muslim].
2. Sincere prayers result in forgiveness of sins
Allah's Apostle said, "Whoever establishes the prayers on the night of Qadr out of sincere faith and hoping to attain Allah's rewards (not to show off) then all his past sins will be forgiven." , Volume 1, Book 2, Number 34, Narrated Abu Huraira
Allah's Apostle said: "Whoever establishes prayers during the nights of Ramadan faithfully out of sincere faith and hoping to attain Allah's rewards (not for showing off), all his past sins will be forgiven." - , Volume 1, Book 2, Number 36, Narrated Abu Huraira
Abu Umama al-Bahili (Allah be pleased with him) reports that the Messenger of Allah (blessings and peace be upon him, his family, and companions) said, Hold fast to night prayer, for it was the way of the righteous before you, a way of drawing closer to your Lord, an expiation for wrong deeds, and a shield from sin. [Tirmidhi, and others]
Abu Hurairah (RA) narrated that Allah’s Messenger (SAW), said: 'The nearest a slave can be to his Lord is when he is prostrating, so invoke (supplicate) Allah (SWT) much in it. [Muslim, abu Dawud, an-Nasa'i and others, Sahih al-Jami #1175]
The prophet (sallallaahu 'alaihi wa sallam) would say among other remembrances of Allaah and supplications in the posture of sujood (prostrating): O Allaah! Forgive me all my sins: the minor and the major, the first and the last, the open and the hidden. [Muslim]
3. Fasting results in forgiveness
Allah's Apostle said, "Whoever observes fasts during the month of Ramadan out of sincere faith, and hoping to attain Allah's rewards, then all his past sins will be forgiven." - Volume 1, Book 2, Number 37, Narrated Abu Huraira.
4. Ablutions and pure thoughts during prayer result in forgivness.
(the slave of 'Uthman) I saw 'Uthman bin 'Affan asking for a tumbler of water (and when it was brought) he poured water over his hands and washed them thrice and then put his right hand in the water container and rinsed his mouth, washed his nose by putting water in it and then blowing it out. then he washed his face and forearrlns [sic] up to the elbows thrice, passed his wet hands over his head and washed his feet up to the ankles thrice. Then he said, "Allah's Apostle said 'If anyone Performs ablution [washing] like that of mine and offers a two-rak'at prayer [spiritual communication with Allah] during which he does not think of anything else (not related to the present prayer) then his past sins will be forgiven.' " After performing the ablution 'Uthman said, "I am going to tell you a Hadith which I would not have told you, had I not been compelled by a certain Holy Verse (the sub narrator 'Urwa said: This verse is: "Verily, those who conceal the clear signs and the guidance which we have sent down...)" (2:159). I heard the Prophet saying, 'If a man performs ablution perfectly and then offers the compulsory congregational prayer, Allah will forgive his sins committed between that (prayer) and the (next) prayer till he offers it. Volume 1, Book 4, Number 161, Narrated Humran, See also 165
Uthman reported, God's Messenger having said: "If any one performs the ablutions well, his sins will come out of his body and even from his nails."
5. Prayer offered in a congregation is 25 times better than prayer offered alone and each step towards a mosque results in forgiveness of a sin.
The Prophet said, "The prayer offered in congregation is twenty five times more superior (in reward) to the prayer offered alone in one's house or in a business center, because if one performs ablution and does it perfectly, and then proceeds to the mosque with the sole intention of praying, then for each step which he takes towards the mosque, Allah upgrades him a degree in reward and (forgives) crosses out one sin till he enters the mosque. When he enters the mosque he is considered in prayer as long as he is waiting for the prayer and the angels keep on asking for Allah's forgiveness for him and they keep on saying: 'O Allah! Be Merciful to him, O Allah! Forgive him, as long as he keeps on sitting at his praying place and does not pass wind. (See Hadith No. 620). Volume 1, Book 8, Number 466, Narrated Abu Huraira,
6. Prayers coinciding with that of angels results in forgiveness of sins.
The Prophet said, "Say Amin" when the Imam says it and if the Amin of any one of you coincides with that of the angels then all his past sins will be forgiven." Ibn Shihab said, "Allah's Apostle used to Say "Amin." Volume 1, Book 12, Number 747, Narrated Abu Huraira, See also 748.
“The angels that bear the Throne and those that are around to extol your Lord’s glory with His praise, they believe in Him, and ask forgiveness for the believers, saying: “Our Lord! You encompass everything with Your Mercy and Knowledge. So forgive those that repent and follow Your Path, and guard them against the chastisement of Hell” (40:7).
7. If you recite a certain prayer and die that day, your sins will all be forgiven.
The Prophet said "The most superior way of asking for forgiveness from Allah is: 'Allahumma anta Rabbi la ilaha illa anta, Anta Khalaqtani wa ana abduka, wa ana 'ala ahdika wa wa'dika mastata'tu, A'udhu bika min Sharri ma sana'tu, abu'u Laka bini'matika 'alaiya, wa Abu Laka bidhanbi faghfirli innahu la yaghfiru adhdhunuba illa anta." [O' my god You are my Lord, there is no god but You. You created me, and I am your bondservant, and I will stick to my covenant and promise [of faith and sincere obedience] to You, as to my ability. I seek refuge in You from the evil of what I have done, I acknowledge, to You, your bounties upon me, and I acknowledge, to You, my sin. Thus forgive me, for none forgives sins except You.] The Prophet added. "If somebody recites it during the day with firm faith in it, and dies on the same day before the evening, he will be from the people of Paradise; and if somebody recites it at night with firm faith in it, and dies before the morning, he will be from the people of Paradise." Volume 8, Book 75, Number 318, Narrated Shaddad bin Aus, See also 335:
8. Increased remembrance of Allah.
Allah's Apostle said,"Whoever says: "La ilaha illal-lah wahdahu la sharika lahu, lahu-l-mulk wa lahu-l-hamd wa huwa 'ala kulli shai'in qadir," one hundred times will get the same reward as given for manumitting ten slaves; and one hundred good deeds will be written in his accounts, and one hundred sins will be deducted from his accounts, and it (his saying) will be a shield for him from Satan on that day till night, and nobody will be able to do a better deed except the one who does more than he." Narrated Abu Huraira: Volume 8, Book 75, Number 412.
Allah's Apostle said, "Whoever says, 'Subhan Allah wa bihamdihi,' one hundred times a day, will be forgiven all his sins even if they were as much as the foam of the sea," Volume 8, Book 75, Number 414, Narrated Abu Huraira
9. Forgive others to be forgiven
The Messenger of Allah said: "The best deed before Allah is to pardon a person who has wronged you, to show affection for relatives who have broken ties with you, and to act generously towards a person who has deprived you". Thereafter he recited the following holy verses: "Turn to forgiveness and enjoin good and turn aside from ignorant" (7:199).
A'isha(may Allah be pleased with her) said that God's Messenger(salallahu alahyi wa sallam) never took revenge on his own behalf on anyone. She also said that God's Messenger was not unseemly or obscene in his speech, nor was he loud-voiced in the streets, nor did he return evil for evil, but he would forgive and pardon.
'Abdullah ibn al-'As reported that the Prophet, may Allah bless him and grant him peace, said, "Show mercy and you will be shown mercy. Forgive and Allah will forgive you. Woe to the vessels that catch words (i.e. the ears). Woe to those who persist and consciously continue in what they are doing." Bukhari 380
'Umar was heard to say, "Anyone who does not show mercy will not be shown mercy. Anyone who does not forgive will not be forgiven. Anyone who does not turn in repentance will not be turned to nor will he be protected or guarded." Bukhari 372
Jarir reported that the Prophet, may Allah bless him and grant him peace, said, "Allah will not show mercy to a person who does not show mercy to other people." Bukhari 375
Abu Hurayra reported that the Messenger of Allah, may Allah bless him and grant him peace, said, "One day a man became very thirsty while walking down the road. He came across a well, went down into it, and drank and then climbed out. In front of him he found a dog panting, eating the dust out of thirst. The man said, 'This dog is as thirsty as I was.' He went back down into the well and filled his show, putting it into his mouth (in order to climb back up) and then gave the dog water. Therefore Allah thanked him and forgave him." They said, "Messenger of Allah, will we have a reward on account of animals?" He said, "There is a reward on account of every living thing." Bukhari 378
'Abdullah ibn 'Umar reported that the Messenger of Allah, may Allah bless him and grant him peace, said, "A woman punished her cat by imprisoning it until it died of hunger and because of it, she entered the Fire. It was said ¬ and Allah knows best: 'You did not feed it nor give it water when you imprisoned it nor did you release it and let it eat from the plants of the earth." Bukhari 379
Abu Umama that the Messenger of Allah, may Allah bless him and grant him peace, said, "Anyone who shows mercy, even to an animal meant for slaughtering, will be shown mercy by Allah on the Day of Rising." Bukhari 381
10. Increase good deeds to erase bad deeds
The prophet (S.A.W.) emphasizes to us that good deeds wipe out bad ones. This is expressed in many authentic Ahadith. The prophet (S.A.W.) said to Abu Tharr (R.A.): "...And follow the bad deed with a good one that will wipe out the bad one…." In another narration, Abu Tharr asked the prophet (S.A.W.): "Give me advice", the prophet (S.A.W.) said: "If you do a bad deed, then follow it with a good one that will wipe it out." Abu Tharr said: "Oh Messenger of Allah, is "La Ilaha Illa Lah" from the good deeds" The prophet (S.A.W.) replied: "It is the best deed."
In an authentic Hadith reported by Imam At-Tirmithi that the prophet (S.A.W.) said: "The charity puts out the bad deed like the water puts out the fire."
And keep up prayer in the two parts of the day and in the first hours of the night; surely good deeds take away evil deeds this is a reminder to the mindful. [11.114]
Except him who repents and believes and does a good deed; so these are they of whom Allah changes the evil deeds to good ones; and Allah is Forgiving, Merciful. [25.70]
11. Sincere repentance & making amends earns forgiveness
And most surely I am most Forgiving to him who repents and believes and does good, then continues to follow the right direction. [20.82]
Imam Muslim reported that the prophet (S.A.W.) said, "If anyone repents before the sun rises from the west, Allah will forgive him."
And also in An authentic Hadith reported by Imam At-Tirmidhi that the prophet (S.A.W.) said, "Allah accepts a slave's repentance till his death rattle begins (That is, before the soul of the dying person reaches the throat)."
Hadith Qudsi: Allah, the Almighty, has said: O Son of Adam, so long as you call upon Me and ask of Me, I shall forgive you for what you have done, and I shall not mind. O Son of Adam, were your sins to reach the clouds of the sky and were you then to ask forgiveness of Me, I would forgive you. O Son of Adam, were you to come to Me with sins as great as the earth, and were you then to face Me ascribing no partners to Me, I would bring you forgiveness nearly as great as it.
Except those who repent and amend and make manifest (the truth), these it is to whom I turn (mercifully); and I am the Oft-returning (to mercy), the Merciful. [2.160]
Repentance with Allah is only for those who do evil in ignorance, then turn (to Allah) soon, so these it is to whom Allah turns (mercifully), and Allah is ever Knowing, Wise.
And repentance is not for those who go on doing evil deeds, until when death comes to one of them, he says: Surely now I repent; nor (for) those who die while they are unbelievers. These are they for whom We have prepared a painful chastisement. [4.17-18]
Except those who repent and amend and hold fast to Allah and are sincere in their religion to Allah, these are with the believers, and Allah will grant the believers a mighty reward. [4.146]
The Noble Prophet Muhammad (saw) said: "The sign of the people of Hell is mostly because of the postponement of repenting (Tawbah and Istighfar)."
The Noble Prophet Muhammad (saw) said: "A sincere repentant never sins again as the milk drawn from the breast never can go back to its source."
The Noble Prophet Muhammad (saw) said: "The repentant from a sin is as same as him who did not commit it."
The Noble Prophet Muhammad (saw) said: "Nothing is more favorable to Allah (SWT) than a male or female repentant believer."
The Noble Prophet Muhammad (saw) said: "There are four signs of one who is repentant: (1) He is sincere to Allah (SWT) in his actions (2) He shuns falsehood (3) He is firmly attached to truth and (4) He is eager to do good."
Imam Ali (as) said: "The sin that makes you sad and repentant is more liked by Allah (SWT) than the good deed which turns you arrogant."
Imam Ali (as) said: "A sincere repentant: (1) is ashamed of his past sins (2) takes up the duties overlooked and fulfils them (3) makes good the willfully ignored conditions of a trust managed by him (4) forgives those who provoke him (5) does not demand repayment of loans from those who are in financial distress (6) makes firm determination not to sin ever again (7) surrenders his self to the adoration, devotion and service of Allah (SWT) when it had swelled to the point of exploding due to inordinate consumption of worldly pleasures, transgression and disobedience."
[6.54] And when those who believe in Our communications come to you, say: Peace be on you, your Lord has ordained mercy on Himself, (so) that if any one of you does evil in ignorance, then turns after that and acts aright, then He is Forgiving, Merciful.
12. Following the Sunnah of the Prophet (The Straight Path) leads to forgiveness
O you who believe! be careful of(your duty to) Allah and speak the right word, He will put your deeds into a right state for you, and forgive you your faults; and whoever obeys Allah and His Apostle, he indeed achieves a mighty success. [33.70-71]
Say: If you love Allah, then follow me, Allah will love you and forgive you your faults, and Allah is Forgiving, MercifuL Say: Obey Allah and the Apostle; but if they turn back, then surely Allah does not love the unbelievers. [3.31-32]
Those who follow the Apostle-Prophet, the Ummi, whom they find written down with them in the Taurat and the Injeel (who) enjoins them good and forbids them evil, and makes lawful to them the good things and makes unlawful to them impure things, and removes from them their burden and the shackles which were upon them; so (as for) those who believe in him and honor him and help him, and follow the light which has been sent down with him, these it is that are the successful. Say: O people! surely I am the Apostle of Allah to you all, of Him Whose is the kingdom of the heavens and the earth there is no god but He; He brings to life and causes to die therefore believe in Allah and His apostle, the Ummi Prophet who believes in Allah and His words, and follow him so that you may walk in the right way. [7.157-158]
Say: I am only a mortal like you; it is revealed to me that your God is one God, therefore follow the right way to Him and ask His forgiveness; and woe to the polytheists [41.6]
[6.155] And this is a Book We have revealed, blessed; therefore follow it and guard (against evil) that mercy may be shown to you.
[6.48] And We send not messengers but as announcers of good news and givers of warning, then whoever believes and acts aright, they shall have no fear, nor shall they grieve.