Banu Sulaym
The Muslims Muhammad dispatched toward the Najd were subsequently slain at a well called Bir Ma'una in the territory of the Banu Sulaym, for which the Islamic tradition generally implicated Abu Bara's nephew and leadership rival Amir ibn al-Tufayl. The traditional accounts held that the Banu Amir refused to participate in the assault due to Abu Bara's promise of protection, so Amir ibn al-Tufayl called on the Banu Sulaym instead. Two Kilabi tribesmen, who had been given Muhammad's protection, were killed in revenge by the surviving Muslims on their return from Bir Ma'una to Medina, who were not aware of Muhammad's protection of them. Muhammad subsequently paid blood money to Abu Bara as compensation. The historian M. J. Kister assessed that Abu Bara, then an elderly man, cooperated with Muhammad because Muslim support would strengthen his position in the tribe against Amir ibn al-Tufayl. Muhammad, meanwhile, hoped to gain adherents to the Muslim cause among the powerful Banu Amir.