When two Muslims meet to fight each other with their swords, both the killer and the killed are doomed to Hellfire

The Prophet (may Allah's peace and blessings be upon him) informs that if two Muslims fight each other with their swords, with each one intending to kill the other, the killer will be in Hellfire for the actual killing of his companion; but the Companions were confused regarding the killed one and why he would be in Hellfire!

The Prophet (may Allah's peace and blessings be upon him) explained that he, too, would be in Hellfire because of his keenness to kill his companion and that nothing prevented him except that his companion managed to kill him first.