Musannaf Ibn Abi Shayba 13:2686

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Al-Walid ibn ‘Isa al-Sa’di narrated to us, he said: I said to al-Hasan: "We have billy goats that we rent out." He said: "There is no harm in it, as long as they are not milked or their udders are massaged."