Maliks Muwatta Book 31, Hadith Number 59.
Section : What is Permitted in Selling Some Animals for Others and Making an Advance for Them.
Yahya related to me from Malik from Salih ibn Kaysan from Hasan ibn Muhammad ibn Ali ibn Abi Talib that Ali ibn Abi Talib sold one of his camels called Usayfir for 20 camels to be delivered later.