Musannaf Ibn Abi Shayba 28:1173

'Abd al-Rahim ibn Sulayman narrated to us, from Muhammad ibn Ishaq, from Yazid ibn Abi Habib, from 'Abd al-'Aziz ibn Abi al-Sa'ba, from Abu Aflah al-Hamdani, from 'Abd Allah ibn Zurayr al-Ghafiqi, from 'Ali, who said: A white mule was gifted to the Messenger of Allah, may Allah bless him and grant him peace. I said, "O Messenger of Allah, if we wished, we could breed from this [mule]." He said, "And how?" We said, "We would mount the Arabian horses [upon the female mules] and they would produce [offspring] by them." He said, "Only those who do not know do that."