It is narrated from Sayyiduna Abdullah (may Allah be pleased with him), he says: When a man says to his companion, "You are my enemy," then one of them goes out of Islam, or he becomes disassociated from his companion. Qais (may Allah have mercy on him) says that later Abu Juhaifah informed me that Abdullah (may Allah be pleased with him) said: Yes, if he repents (then it is another matter).