Short answer
It depends on why and what you report. Reporting someone to stop harm to others, such as abuse, theft, violence or bullying, is allowed and can be a duty. Exposing someone's private sins that harm only themselves is disliked: Islam prefers that you cover them and advise privately. Carrying tales to cause trouble (namimah) is haram.
Informing those in authority to prevent harm or wrong against others is permitted, and becomes required when it is the only way to stop the harm. Concealing a private sin and advising the person is better. Spying and tale-carrying to stir trouble are haram.
The four schools agree on this.
Explanation
The word 'snitching' mixes together very different acts. Islam judges each one by its aim and its effect.
Stopping harm to others. The Prophet ﷺ said: help your brother whether he is an oppressor or oppressed. Asked how to help an oppressor, he said: by stopping him. Reporting a classmate who is bullying someone, a person stealing at work, or abuse of a child is helping both the victim and the wrongdoer. Allah tells believers to stand firm for justice, even against themselves or their relatives. If reporting is the only way to stop serious harm, staying silent shares in the wrong.
Private sins. If someone sins in private and harms only himself, the sunnah is to cover him and advise him quietly. The Prophet ﷺ said whoever covers a Muslim, Allah will cover him in this world and the next. The Hanafi jurists even say that a witness to a hadd offence may choose between testifying and concealing, and concealing is better. So running to parents, teachers or social media to expose a friend's private sin is not the Islamic way.
Tale-carrying. Passing on what people say to cause fights is namimah, and the Prophet ﷺ said the tale-carrier will not enter Paradise. Spying on people to find faults is forbidden in the Quran.
Before you report, ask:
- Is anyone being harmed, or at risk?
- Have I tried advising the person first, if that is safe?
- Am I sure of the facts? Allah warns against acting on unverified news.
- Am I going to the right person, someone who can stop the harm, not just spread it?
The four schools agree on these principles. See also what is backbiting.
The evidence
Quran, Surah An-Nisaa 4:135
۞ يَٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ كُونُوا۟ قَوَّٰمِينَ بِٱلْقِسْطِ شُهَدَآءَ لِلَّهِ وَلَوْ عَلَىٰٓ أَنفُسِكُمْ أَوِ ٱلْوَٰلِدَيْنِ وَٱلْأَقْرَبِينَ ۚ إِن يَكُنْ غَنِيًّا أَوْ فَقِيرًۭا فَٱللَّهُ أَوْلَىٰ بِهِمَا ۖ فَلَا تَتَّبِعُوا۟ ٱلْهَوَىٰٓ أَن تَعْدِلُوا۟ ۚ وَإِن تَلْوُۥٓا۟ أَوْ تُعْرِضُوا۟ فَإِنَّ ٱللَّهَ كَانَ بِمَا تَعْمَلُونَ خَبِيرًۭا ﴿١٣٥﴾
O you who have believed, be persistently standing firm in justice, witnesses for Allah, even if it be against yourselves or parents and relatives. Whether one is rich or poor, Allah is more worthy of both. So follow not [personal] inclination, lest you not be just. And if you distort [your testimony] or refuse [to give it], then indeed Allah is ever, with what you do, Acquainted.
Justice can require speaking up, even against people close to you.
Quran, Surah Al-Hujuraat 49:12
يَٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ ٱجْتَنِبُوا۟ كَثِيرًۭا مِّنَ ٱلظَّنِّ إِنَّ بَعْضَ ٱلظَّنِّ إِثْمٌۭ ۖ وَلَا تَجَسَّسُوا۟ وَلَا يَغْتَب بَّعْضُكُم بَعْضًا ۚ أَيُحِبُّ أَحَدُكُمْ أَن يَأْكُلَ لَحْمَ أَخِيهِ مَيْتًۭا فَكَرِهْتُمُوهُ ۚ وَٱتَّقُوا۟ ٱللَّهَ ۚ إِنَّ ٱللَّهَ تَوَّابٌۭ رَّحِيمٌۭ ﴿١٢﴾
O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin. And do not spy or backbite each other. Would one of you like to eat the flesh of his brother when dead? You would detest it. And fear Allah; indeed, Allah is Accepting of repentance and Merciful.
Spying to find people's faults is forbidden.
Sahih al-Bukhari 2444
Sahih... انصر أخاك ظالما أو مظلوما ...
"Help your brother whether he is an oppressor or oppressed."
Stopping a wrongdoer, including by reporting him, is helping him.
Sahih Muslim 2699
Sahih... ومن ستر مسلما ستره الله في الدنيا والآخرة ...
"Whoever covers a Muslim, Allah will cover him in this world and the Hereafter."
Private sins should be covered, not exposed.
Sahih al-Bukhari 6056
Sahih... لا يدخل الجنة قتات ...
"The tale-carrier will not enter Paradise."
Passing on words to cause trouble is a major sin.
Where the ruling is recorded
- al-Hidaya, Kitab al-Shahadat. In hadd offences the witness may choose between testifying and concealing, and concealing is better; in people's rights, testimony is required when asked.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. 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.