Musnad Abu Ya'la al-Mawsili 42:120

Abu Bakr narrated to us, 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 al-Khudri, who said: The Messenger of Allah (may Allah bless him and grant him peace) forbade the purchasing of what is in the bellies of livestock until they give birth, and what is in their udders except by measurement. He also forbade the purchasing of a slave while he is a runaway, the purchasing of war spoils until they are divided, the purchasing of charity (zakat) items until they are collected, and the "diver's strike" (a form of gambling/uncertain transaction).