Assalamu'alaikum.
The meaning of Bid'a is : Innovation in Ibadah [worship, i.e. all acts of submission to Allah, as defined in Qur'an and Sunnah]
Some examples of bid'a (innovation):
~Fasting on only Friday (see Bukhari 3:205), on the day of breaking the Ramadan fast (see Bukhari 3:211), or the first day of 'Id ul Fitr and 'Id ul-Adha (see Bukhari 3:211, 213)
~The use of dhikr beads when doing dhikr
The Prophet (peace be upon him) commanded them (the women emigrants) to be regular (in remembering Allah by saying): "Allah is most great"; "Glory be to the King, the Holy"; "there is no god but Allah"; and that they should count them on fingers, for they (the fingers) will be questioned and asked to speak. [Dawood 1496, Narrated Yusayrah, mother of Yasir]
~Placing trust in witchcraft
~Eating donkey meat (see Bukhari 5:511), or animals with fangs (see Bukhari 7:672)
~Drinking out of a gold or silver cup, or eating on a gold or silver plate (see Bukhari 7:337, 722)
~Males wearing silk (see Bukhari 7:718)
~Making du'a while facing a grave (i.e. intentions to seek help in any way from the deceased, whether a prophet or not)
~Celebrating the dunya's(world's matter) holidays
~Celebrating the Prophet saaws' birthday, i.e. Milaad
~Declaring haram (forbidden) something that is not declared haram in the Qur'an or Sunnah
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When presenting Islam to someone, present Qur'an, not your opinion.
Said Mujahid, "We were in a meeting in the mosque with the companions of Ibn 'Abbas (Tawus, Sa'eed ibn Jubair and 'Ikrimah). When he stood to pray, a man came in and said, 'Is there one who can give a legal verdict?' We said, 'Ask your question.' He said, 'Whenever I urinate, a liquid always follows it.' We asked, 'Is it the type of liquid that gives birth to children?' He said, 'Yes.' We said, 'Then you have to perform ghusl.' The man went away. Ibn 'Abbas hurried to finish his prayer, after which he told 'Ikrimah to bring the man back. He turned to us and said, 'Is your verdict found in the Book of Allah?' We said, 'No.' He asked, 'Is it based on the sayings of the Prophet, upon whom be peace?' We said, 'No.' 'Then from what?' We said, 'From our opinion.' He said, 'That is why the Messenger of Allah said that one learned man is more difficult for Satan than a thousand worshippers.' The man came and faced Ibn 'Abbas, who said to him, 'When that happens, is it owing to any stimulation?' He answered, 'No.' Ibn 'Abbas asked, 'Do you feel any numbness in your body?' He answered, 'No.' Said Ibn 'Abbas, 'That is from the cold. Ablution is sufficient."'
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