Sunan an-Nasa'i 4120
سنن النسائي#4120SahihIt was narrated from Abu Bakrah that :The Prophet [SAW] said: "If two Muslims confront each other with swords, each of them wanting to kill the other, they will both be in Hell." It was said to him: "O Messenger of Allah, (we understand about) the killer, but what about the one who is killed?" He said: "He was determined 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
In-book reference: 37:155