Sahih Muslim Book 54, Hadith 20
This hadith has been narrated on the authority of Hammad through another chain of transmitters.
When two Muslims confront each other with their swords, both the slayer and the slain are doomed to Hell-Fire.
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.