Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) relates that the Prophet (peace and blessings be upon him) summoned Sayyiduna Sa'd bin Mu'adh (may Allah be pleased with him) concerning the matter of Banu Qurayzah. Sa'd (may Allah be pleased with him) came riding a donkey, on which his feet nearly touched the ground. When the Prophet (peace and blessings be upon him) saw him, he said to his Companions: "Stand up for your chief." Then the Prophet (peace and blessings be upon him) said to him: "These people have agreed to your judgement, so judge concerning them." He said: I judge concerning them that their fighting men be killed and their offspring be taken captive. The Prophet (peace and blessings be upon him) said: "You have judged according to the judgement of Allah and the judgement of the King (that is, Allah)."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5304