Sahih Muslim
The Book of Jihad and Expedition (Kitab Al-Jihad wal-Siyar)
Book Number: 019 / Hadith Number: 4368
It has been narrated on the authority of Abu Sa'id al-Khudri who said: The people of Quraiza surrendered accepting the decision of Sa'd b. Mu'adh about them. Accordingly, the Messenger of Allah (may peace be upon him) sent for Sa'd who came to him riding a donkey. When he approached the mosque, the Messenger of Allah (may peace be upon him) said to the Ansar: Stand up to receive your chieftain. Then he said (to Sa'd): These people have surrendered accepting your decision. He (Sa'd) said: You will kill their fighters and capture their women and children. (Hearing this), the Propbot (may peace he tpon him) said: You have adjudged by the command of God. The narrator is reported to have said: Perhaps he said: You have adjuged by the decision of a king.
Ibn Muthanna (in his version of the tradition) has not mentioned the alternative words.