Musannaf Ibn Abi Shayba 13:1954

Abu Bakr narrated to us, he said: Hatim ibn Isma'il narrated to us, from Jahdam ibn 'Abd Allah, from Muhammad ibn Ibrahim, from Muhammad ibn Zayd, from Shahr ibn Hawshab, from Abu Sa'id, he said: The Prophet, may Allah bless him and grant him peace, forbade the purchasing of what is in the bellies of livestock until they give birth, and [he forbade] what is in their udders, except by measurement.