The circumstances of the Qurayza's demise have been related by Ibn Ishaq and other Muslim historians who relied upon his account. According to Watt, Peters and Stillman, the Qurayza surrendered to Muhammad's judgement - a move Watt classifies as unconditional. The Aws, who wanted to honor their old alliance with the Qurayza, asked Muhammad to treat the Qurayza leniently as he had previously treated the Qaynuqa for the sake of Ibn Ubayy. (Arab custom required support of an ally, independent of the ally's conduct to a third party.) Muhammad then suggested to bring the case before an arbitrator chosen from the Aws, to which both the Aws and the Qurayza agreed to. Muhammad then appointed Sa'd ibn Mua'dh to decide the fate of the Jewish tribe.