On forbidding calling a Muslim an unbeliever

Riyad as-Salihin (The Meadows of the Righteous)

by Imam Nawawi

326. Chapter: On forbidding calling a Muslim an unbeliever

1732. Ibn 'Umar reported that the Messenger of Allah, may Allah bless him and grant him peace, said, "When a man says to his brother, 'O unbeliever,' one of them returns with that ascription applying to him. If it is not as the one who said it said, it reverts to him." [Agreed upon]

1733. Abu Dharr heard the Messenger of Allah, may Allah bless him and grant him peace, say, "If anyone calls a man an unbeliever or says, 'enemy of Allah' when that is not the case, that reverts to him." [Agreed upon]