" إِذَا الْتَقَى الْمُسْلِمَانِ بِسَيْفَيْهِمَا فَقَتَلَ أَحَدُهُمَا صَاحِبَهُ فَالْقَاتِلُ وَالْمَقْتُولُ فِي النَّارِ "
It was narrated that Abu Bakrah said: "The Messenger of Allah [SAW] said: 'If two Muslims fight with swords, and one of them kills the other, then the killer and the slain will both be in Hell.'"