(16) باب الدَّلِيلِ عَلَى زِيَادَةِ الإِيمَانِ وَنُقْصَانِهِ
Ibn 'Umar reported the Messenger of Allah (May peace be upon him) as saying :
If any believing man calls another believing man an unbeliever, if he is actually an infidel, it is all right ; if not, he will become an infidel.
Reference: Sunan Abi Dawud 4687
In-book reference: Book 42, Hadith 92
English translation: Book 41, Hadith 4670