Mukhtasar Bukhari

It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that during the time of the Messenger of Allah (peace and blessings be upon him), some Muslims joined the polytheists so that their group would become larger, and then (at the time of battle) an arrow would come and one of them would be killed, or someone would be killed by the strike of a sword. At that time, this verse was revealed: "Indeed, those whom the angels take [in death] while wronging themselves, [the angels] will say, 'In what [condition] were you?...'"