Short answer
A qareen is a companion Allah assigns to every person. The hadith says each of us has a companion from the jinn, who urges toward evil, and a companion from the angels, who urges toward good. The Prophet ﷺ said he had one too, but Allah helped him against it so it only told him good.
Belief in the qareen is part of Sunni belief because it comes in a sahih hadith. It cannot force anyone to sin: it only whispers, and you remain responsible for your choices. Dhikr, seeking refuge in Allah and reciting the Quran weaken its influence.
The four schools agree on this.
Explanation
The Prophet ﷺ said: "There is none of you except that his companion from the jinn has been assigned to him." The Companions asked, "Even you?" He said, "Even me, but Allah helped me against him, so he only tells me to do good." Another narration in Sahih Muslim adds that each person also has a companion from the angels.
The Quran mentions this companion too. Whoever turns away from the remembrance of Allah, "We appoint for him a devil, and he is to him a companion" (43:36). On the Day of Judgement the companion will try to escape blame: "Our Lord, I did not make him transgress, but he [himself] was in extreme error" (50:27). That verse shows the qareen whispers, but the choice to sin is the person's own.
Several popular ideas about the qareen have no basis. It is not a twin or double of you, it is not the ghost of a dead person, and you cannot contact it to learn secrets. People who claim to speak to someone's qareen to reveal hidden things are practising a form of fortune-telling, which Islam forbids.
How do you weaken it? Begin things with bismillah, keep the morning and evening adhkar, say a'udhu billahi minash-shaytanir-rajim when anger or evil thoughts come, and keep up the Quran. See also Jinn in Islam.
The evidence
Quran, Surah Az-Zukhruf 43:36
وَمَن يَعْشُ عَن ذِكْرِ ٱلرَّحْمَٰنِ نُقَيِّضْ لَهُۥ شَيْطَٰنًۭا فَهُوَ لَهُۥ قَرِينٌۭ ﴿٣٦﴾
And whoever is blinded from remembrance of the Most Merciful - We appoint for him a devil, and he is to him a companion.
Shows that turning from Allah's remembrance strengthens the devil companion.
Quran, Surah Qaaf 50:27
۞ قَالَ قَرِينُهُۥ رَبَّنَا مَآ أَطْغَيْتُهُۥ وَلَٰكِن كَانَ فِى ضَلَٰلٍۭ بَعِيدٍۢ ﴿٢٧﴾
His [devil] companion will say, "Our Lord, I did not make him transgress, but he [himself] was in extreme error."
Shows the qareen cannot force a person to sin.
Sahih Muslim 2814
Sahih... مَا مِنْكُمْ مِنْ أَحَدٍ إِلاَّ وَقَدْ وُكِّلَ بِهِ قَرِينُهُ مِنَ الْجِنِّ ...
"There is none of you except that his companion from the jinn has been assigned to him."
The main proof that every person has a qareen.
Where the ruling is recorded
- Sharh al-Nawawi ala Sahih Muslim, Book of the descriptions of the hypocrites, the hadith of the qareen. Explains the hadith and the two readings of the Prophet's words about his companion.
- Tafsir Ibn Kathir, Commentary on Surah al-Zukhruf, verse 36. Explains that the devil companion is assigned to the one who turns from Allah's remembrance.
This answer is pending review by the scholars on our team. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.