Who are Banu Qurayza and what happened to them?

The Prophet, peace and blessings be upon him, migrated to Medina, where three Jewish tribes resided: Banu Qaynuqa, Banu al-Nadir, and Banu Qurayza. After they rejected Islam and broke their covenants with him, these tribes fought the Prophet. During the Battle of al-Ahzab (the Confederates), Banu Qurayza violated their treaty with the Muslims and allied themselves with Quraysh and Ghatafan, which intensified the siege on the Muslims.

After Allah thwarted the Confederates with winds and angels, Gabriel commanded the Prophet to head towards Banu Qurayza. The Muslims besieged them until they submitted to the judgment of Sa'd ibn Mu'adh, who ruled that their fighting men should be killed and their women and children enslaved. This judgment was carried out: those men who had grown pubic hair were executed, and those who had not were spared.