As-salaamu'Alaykum,
I am going to close this thread because I think it has served it purpose and now the discussion has altered.
The saheeh ahaadeeth mentioned earlier should make this matter clear. I think the only thing I can say is we should be careful and fear Allah of the implications of what we say can have.
They have no authority over the righteous slaves of Allah
Allah (subhaanahu wa ta'aala) has not given the Shaytaan any power to force people towards misguidance and kufr:
Verily, My slaves (i.e., the true believers of Islamic Monotheism) - you have no authority over them. And All-Sufficient is your Lord as a Guardian.
(Qur'aan 17: 65)
And he (Iblees - Satan) had no authority over them, except that We might test him who believes in the Hereafter, from him who is in doubt it.
(Qur'aan 34: 21)
What this means is that the Shaytaan has no means of gaining power over them, not by means of proof, or of force. The Shaytaan knows this fact:
(Iblees - Satan) said: 'O my Lord! Because You misled me, I shall indeed adorn the path of error for them (mankind) on the earth, and I shall mislead them all.
Except Your chosen, (guided) slaves among them.'
(Qur'aan 15: 39-40)
But he is able to gain control of those people who accept his ideas and who follow him willingly:
Certainly, you shall have no authoirty over My slaves, except those who follow you of the Ghaawoon (Mushrikoon and those who go astray, criminals, polytheists, and evildoers).
(Qur'aan, 15: 42)
On the Day of Resurrection, the Shaytaan will say to his followers whom he misguided and led to their doom:
'I had no authority over you except that I called you, and you responded to me.'
(Qur'aan, 14: 22)
In another aayah:
His power is only over those who obey and follow him (Satan), and those who join partners with Him (Allah, i.e. those who are Mushrikoon).
(Qur'aan, 16: 100)
The power which the Shaytaan has been given over them is the power to deceive, misguide and wield full control over them, so that he pushes them to commit kufr and shirk and he forces them and does not let them leave him, as Allah says:
See you not that We have sent the Shayaateen (devils) against the disbelievers to push them to do evil.
(Qur'aan 19: 83)
The Shaytaan has no evidence or proof of his power over his friends; rather it is simply the matter of their having responded to his call of them, because it suited their whims and desires and their aims. So they are the ones who have helped him against themselves and enabled their enemy to gain power over them by agreeing with him and following him. When they gave in to him willingly and gave him control over themselves, he was given power over them as a punishment to them. Allah does not give the Shaytaan any authority over a person until the person himself opens the way by obeying him and associating him with Allah. Then Allah gives him authority and power over him.
He is given power over the believers because of their sins
In the hadith it says:
"Allah is with the qaadi (judge) so long as he is not unfair. If he judges unfairly, then He forsakes him and lets the Shaytaan be with him."
This is narrated by Al-Haakim and Al-Bayhaqi with a hasan isnad.
(Saheeh al-Jaami', 2/130)
Allah has told us in His Book about a person to whom Allah showed His Signs, and he learned them and understood them, then he forsook all of that, so Allah gave the Shaytaan power over him and he tricked him and misled him, so he became a lesson for others and a story to be told:
And recite (O' Muhammad 
) to them the story of him to whom We gave Our Aayaat, but he threw them away; so Shaytaan (Satan) followed him up, and he became of those who went astray.
And had We willed, We would surely, have elevated him therewith, but he clung to the earth and followed his own vain desire. So his parable is the parable of a dog: if you drive him away, he lolls his tongue out, or if you leave him alone, he (still) lolls his tongue out. Such is the parable of the people who reject Our Aayaat (proofs, evidences, verses, lessons, signs, revelations). So relate the stories, perhaps they may reflect.
(Qur'aan, 7: 175-176)
(The World of the Jinn and Devils)
Question
The Messenger of Allah said,
"Indeed the Shaytaan indeed flows through the son of Adam just as blood flows through him.'
(Musnad Ahmad, no. 3/159)
Is the flowing described here physical or spiritual?
Answer
Though we don't see it, and though we don't know the reality of it, the flowing described is physical and real. At some level, there is a mixture, whereby a Jinn mixes with and enters the body of a human, and the effects of that are seen in man's actions and behaviour. Not of his own accord, a man may at times even act or speak, and when this happens, it means that a Jinn has gained a kind of control over his mind and will. This possession indicates Allahs ability, whereby He Almighty has given Jinn the ability to cause damage to man, even though man neither feels nor sees what is happening to him. But then if the Qur'aan and other invocations are read over him, the Jinn exits his body - by Allahs permission - and he returns to normal.
Ibn 'Uthaymeen (rahimahullaah)
(Fatawa Islamiyah, Vol. 7, Hadith, pg. 212)
Insha'Allaah I hope I can create a thread in relation to the Jinn and the Devils one day.
Walaykum Salaam.
