صحيح مسلم بالإنكليزيةBook 1: The Book of Faith (Kitab Al-Iman) › Chapter 27: THE CONDITION OF THE FAITH OF ONE WHO CALLS HIS BROTHER MUSLIM AN UNBELIEVER
It is reported on the authority of Ibn 'Umar that the Apostle (may peace and blessings be upon him) observed: When a man calls his brother an unbeliever, it returns (at least) to one of them.
