During the Farewell Pilgrimage, the Messenger of Allah [SAW] asked the people to be quiet and listen, and said: "Do not revert to disbelievers after I am gone, striking the necks of one another (killing one another)."
أَنَّ رَسُولَ اللَّهِ ﷺ فِي حَجَّةِ الْوَدَاعِ اسْتَنْصَتَ النَّاسَ قَالَ لاَ تَرْجِعُوا بَعْدِي كُفَّارًا يَضْرِبُ بَعْضُكُمْ رِقَابَ بَعْضٍ