" إِذَا تَوَاجَهَ الْمُسْلِمَانِ بِسَيْفَيْهِمَا فَقَتَلَ أَحَدُهُمَا صَاحِبَهُ فَهُمَا فِي النَّارِ
It was narrated from Abu Musa Al-Ash'ari that: The Prophet [SAW] said: "If two Muslims confront each other with swords and one of them kills the other, they will both be in Hell."