Sunan an-Nasa'i 4122
سنن النسائي#4122SahihIt was narrated that Abu Bakrah said:"I heard the Messenger of Allah [SAW] say: 'If two Muslims confront each other with their swords and one of them kills the other, both the killer and the slain will be in Hell.'" They said: "O Messenger of Allah, (we understand about) the killer, but what about the one who is killed?" He said: "He wanted to kill his companion
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih - Agreed Upon
In-book reference: 37:157