The Book of Jihad and Expedition (Kitab Al-Jihad wa'l-Siyar)
Muslim :: Book 19 : Hadith 4371
It has been narrated on the authority of Hisham (who learnt it from his father) that the Messenger of Allah (may peace be upon him) said (to Sa'd): You have adjudged their case with the judgment of God. the Exalted and Glorified.