Ahnaf b. Qais reported
I set out with the intention of helping this person (Hadrat 'Ali) when Abu Bakra met me. He said: Ahnaf, where do you intend to go? I said: I intend to help the cousin of Allah's Messenger (ﷺ), viz. 'Ali. Thereupon he said to me: Ahnaf, go back, for I heard Allah's Messenger (ﷺ) as saying: When two Muslims confront one another with swords (in hand) both the slayer and the slain would be in Fire. He (Ahnaf) said: I said, or it was said: Allah's Messenger, it may be the case of one who kills. but what about the slain (why he would be put in Hell-Fire)? Thereupon he said: He also intended to kill his companion.
Ahnaf b. Qais reported on the authority of Abu Bakra that Allah's Messenger (ﷺ) said
When two Muslims confront each other with their swords, both the slayer and the slain are doomed to Hell-Fire.
This hadith has been narrated on the authority of Hammad through another chain of transmitters.
Abu Bakra reported Allah's Messenger (ﷺ) as saying
When two Muslims (confront each other) and the one amongst them attacks his brother with a weapon, both of them are at the brink of Hell-Fire. And when one of them kills his companion, both of them get into Hell-Fire.
Abu Huraira reported Allah's Messenger (ﷺ) many ahadith and one of them was this
The last Hour will not come until the two parties (of Muslims) confront each other and there is a large-scale massacre amongst them and the claim of both of them is the same.
Abu Huraira reported Allah's Messenger (ﷺ) as saying
The last Hour will not come unless there is much bloodshed. They said: What is harj? Thereupon he said: Bloodshed. bloodshed.