Musannaf Ibn Abi Shayba 28:768

Abdullah ibn Idris narrated to us, from Kahmas, from Ibn Sirin, who said: Anas ibn Malik went on a military expedition with Ubaydullah ibn Ziyad. He said: So he gave him thirty heads from the captives of the Jahiliyyah. He said: Then Anas asked him to make them part of the khums (the one-fifth share), but Anas refused to accept them.