Musannaf Ibn Abi Shayba 20:50

Abu Bakr narrated to us, he said: Ibn Idris narrated to us, from ‘Asim ibn Kulayb, from his father, who said: I came to ‘Umar, may Allah be pleased with him, while he was at the seasonal gathering (al-mawsim) behind the tent. I said: "I am so-and-so, son of so-and-so, the Jurmi, and a nephew of ours is a captive among the tribe of so-and-so, and we have presented to him the judgment of the Messenger of Allah, may Allah bless him and grant him peace." He said: And we used to say that the judgment was four camels.