Explanation of the report of Ibn Mas'ud (may Allah be pleased with him): (If a man says to his companion, "You are my enemy," then one of them has exited Islam).

The Shaykh : The second report is authentic in its chain of narration, and it is also a report stopping at a Companion, narrated by the author (may Allah have mercy on him) from Qays. He said: Abdullah said: "If a man says to his companion: 'You are my enemy,' then one of them has exited Islam, or has disavowed his companion."
Qays, from whom this is narrated, is a man from the Tabi'un (the generation after the Companions), namely Ibn Abi Hazim al-Bajali al-Kufi. He says: Abdullah said, and Abdullah is our companion Abdullah ibn Mas'ud (may Allah be pleased with him), a noble Companion. He also narrates to us a high wisdom, which is derived from some of the authentic hadiths. Abdullah said: "If a man says to his companion: 'You are my enemy,' then one of them has exited Islam." Because the meaning of "my enemy" is that we do not meet in Islamic brotherhood . So if a Muslim says to his brother: "You are my enemy, O my enemy," then one of them has exited Islam. Therefore he said: "Then one of them has exited Islam, or has disavowed his companion." Because the one who says to his companion "You are my enemy" is either truthful or a liar. If he is truthful, then this one has disavowed that one, because disbelief and Islam do not coexist. If he is a liar, the situation is reversed, and the statement remains that he is an enemy to the speaker despite his Islam, and this speaker has disavowed [Islam] because he wrongs his Muslim companion by saying "You are my enemy," thus disavowing Islam. This meaning is taken from the authentic hadith in al-Bukhari and others: , . Either he says the truth about his companion, in which case, as long as he spoke the truth, his companion is a disbeliever; or if he was a tyrant and wrongdoer, this interpretation returns, and he turns away from his companion to himself, and he disbelieves by accusing his Muslim brother of disbelief. Therefore, we should take a lesson from here, which is that we should not accuse one another with words that involve transgression, injustice to the other, and describing him with what is not in him. If the Messenger (peace and blessings be upon him) said in the authentic hadith: . They said: O Messenger of Allah, what if he has what you said? He said: ; meaning you fabricated it against him. The greatest lie below this lie is every other lie. The greatest lie is that you say to your Muslim brother: "O disbeliever." If you say to your Muslim brother "O disbeliever," then one of them has disavowed the other, and it is necessary, because Islam and disbelief do not coexist. Either he is truthful in his statement, in which case he has disavowed the one he said "O disbeliever" to, because he has become a disbeliever; or he is a liar in his accusation, in which case the disbelief returns to the accused, and he is disavowed from that one, because this is disbelief and that one remained upon his Islam. So fear Allah, or let every Muslim fear Allah in the rights of his Muslim brother, and not accuse him of what is not in him, especially of disbelief, which is the greatest of major sins. Qays said: And Abu Juhaifah informed me that Abdullah said: "Except for one who repents." Of course, repentance erases the sin. So if a person says to his Muslim brother "O disbeliever," and then it becomes clear to him that he was mistaken in that, or was hasty, or was angry, or was in a state that is not sound, and he becomes aware of this bad state, then he seeks forgiveness from Allah (Mighty and Majestic) and turns to Him and repents. Allah (Mighty and Majestic) accepts repentance from His servants and forgives much.