Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) narrates: The Prophet Muhammad (peace and blessings be upon him) said: "Whenever a person calls another person a disbeliever, then that disbelief returns to one of the two. If the (other person) is indeed a disbeliever (then it is correct), otherwise the first person, due to calling him a disbeliever, himself becomes a disbeliever."