Forbidding Calling a Muslim an Unbeliever

824. Ibn Umar, may Allah be pleased with him, reported that the Messenger of Allah, peace and blessings be upon him, 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.” (Sahih al-Bukhari, Adab, 73; Sahih Muslim, Iman, 111).

 

Nawawi, Imam. Riyad As-Salihin; The Gardens of the Righteous: A collection of authentic hadiths. Tughra Books Press, Inc. 2014