Musannaf Ibn Abi Shayba 13:2457

Abu Bakr narrated to us, he said: Yazid bin Harun narrated to us, from Hajjaj, from Umayr bin Sa'id, he said: We used to give the owners of sheep [the animals] on the condition that they give us such and such amount of cheese, and such and such amount of clarified butter, and such and such amount of whey. So I asked Alqama, Masruq, and Abd al-Rahman bin Abi Layla, and all of them forbade me from it.