Sahih Muslim Book 19, Hadith Number 4369.

Chapter : Justification for killing those guilty of breach of trust and making the people of the fort surrender on the arbitration of a just person.

Through the same chain of transmitters Shu’ba has narrated the same tradition in which he says that the Messenger of Allah (may peace be upon him) said (to Sa’d): You have adjudged according to the command of God. And once he said: you have adjudged by the decision of a king.