The word jinn comes from an Arabic root meaning hidden from sight. The world of the jinn is an independent and separate world, with its own distinct nature and features that are hidden from the world of humans. Jinns and humans have some things in common, such as the possession of understanding and the choice between the way of good and the way of evil.
Allaah has created different types of jinn. Among them are some who can take on different forms, such as dogs and snakes; some who are like flying winds with wings; and some who can travel and rest. Abu Thalabah al-Khushani said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said:
The jinn are of three types:
a types that has wings, and they fly through the air; a type that looks like snakes and dogs; and a type that stops for a rest then resumes its journey.
(Reported by al-Tahhaawi in Mushkil al-Athaar, 4/95, and by al-Tabaraani in al-Kabeer, 22/214. Shaykh al-Albaani said in al-Mishkaat (2/1206, no. 4148): al-Tahhaawi and Abul-Shaykh reported it with a saheeh isnaad).
It is possible for jinn to possess humans. Allah says in His Book (Interpretation of the meaning):
“Those who eat riba [usury] will not stand (on the Day of Resurrection) except like the standing of a person beaten by shaytan leading him to insanity.” [2:275]
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
The fact that a jinni may enter the body of a human is proven by the consensus of the imams of Ahl al-Sunnah wa’l-Jama’ah (the larger body of Muslims who are upon the prophetic traditions). Allah says (interpretation of the meaning):
“Those who eat riba [usury] will not stand (on the Day of Resurrection) except like the standing of a person beaten by shaytan leading him to insanity.” [2:275]
… and in al-Saheeh it is narrated from the Prophet (peace and blessings of Allah be upon him) that
“The Shaytan flows through the son of Adam like blood.”
End quote. Majmoo’ al-Fatawa.
Possession is a kind of sickness. If a person who has this sickness is rational, then he has the choice and he will be brought to account for his words and actions. But if this sickness has overwhelmed him to the point that he has lost his mind and free will, then he is like one who is insane and is not accountable.
Hence in Arabic the word mass (possession) is used to refer to junoon (insanity). See Lisan al-‘Arab. But if he commits an act of aggression against another when he is insane and destroys his property, for example, then he must pay compensation for that.
See: Zad al-Ma’ad.
It says in al-Mawsoo’ah al-Fiqhiyyah:
The fuqaha (jurists) are unanimously agreed that insanity is like unconsciousness and sleep, rather it is more severe in the loss of free will, and it makes whatever he says invalid. For the one who is sleeping, all his verbal statements, such as divorce, becoming Muslim, turning apostate, selling, buying, etc, are invalid. So it is more appropriate that such statements be invalid in the case of insanity, because the insane person has no power of reasoning or discernment. They quoted as evidence for this the words of the Prophet (peace and blessings of Allah be upon him):
“The Pen has been raised from three: the sleeper until he awakens, the child until he reaches maturity and the insane person until he comes back to his senses.” Narrated by the authors of Sunan with a saheeh isnaad (authentic chain of narration). The same applies to all verbal statements because of the potential for harm.
End quote.
It also says:
With regard to the rights of people such as compensation and the like:
these are not waived, because he is not accountable for them, rather his guardian is responsible for paying financial dues from the wealth of the insane person. If he commits some crimes, he is accountable for them financially but not physically.
If he destroys a person’s property when he is in a state of insanity, compensation must be paid, but if he kills someone there is no qisaas (retaliation), but the diyah (blood money) must be paid.