Musannaf Ibn Abi Shayba 13:1314

Abu Bakr narrated to us, he said: Jarir narrated to us, from Mughira, from Hammad, from Ibrahim, regarding two men who claim an animal that is not in the possession of either of them, and one of them produces two witnesses while the other produces four. He said: It is between them in two halves, because the two [witnesses] necessitate the right.