Was it acceptable for Muhammed to behead the Banu Qurayza tribe?
In a Nutshell:
When putting the story in its historical context, the punishment was compatible with the treaty between the Muslims and Banu Qurayza. During the Battle of the Trench the Jews of Banu Qurayza reneged on the defence agreement, violating their scripture and what would be seen in contemporary international law. They committed treason, deserving capital punishment, something seen in many legal systems. Claims of large numbers of executed people, however, has been historically exaggerated.