Musannaf Ibn Abi Shayba 16:107

Abu Bakr narrated to us, he said: Yahya ibn Wadih narrated to us, from Muhammad ibn Ishaq, from Asim ibn Umar ibn Qatadah al-Zafari, from Salma bint Nasr, from a man from Banu Murrah, who said: I came to the Messenger of Allah (may Allah bless him and grant him peace) and said: "O Messenger of Allah, my most valuable property is donkeys; may I benefit from them?" He said: "Do they not graze in the wilderness and eat the trees?" I said: "Yes." He said: "Then benefit from them."