Musannaf Ibn Abi Shayba 13:3318

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Zakariya narrated to us, from al-Sha’bi, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "The back (of the animal) is to be ridden if it is mortgaged, and the milk of the nursing animal is to be drunk if it is mortgaged. And upon the one who rides and drinks is its maintenance."