They had a treaty with the Muslims not to attack them or collaborate with the enemies against them and they betrayed it and collaborated with the tribe of Ghatafan and Quraish to attack the Muslims in Madinah and kill them all to destroy Islam. After one month of besieging Madinah, they gave up and left and the Prophet salla Allahu alaihi wa sallam executed the men of Bani Quraithah for their treachery.