Musannaf Ibn Abi Shayba 28:1174

'Abd al-Rahim ibn Sulayman narrated to us, from 'Umar ibn Husayl, from 'Amir, who said: A white mule was gifted to the Messenger of Allah, may Allah bless him and grant him peace. Dihya al-Kalbi said: "If we wished, O Messenger of Allah, we could take one like it." He [the Prophet] said: "And how?" He said: "We would mount the donkeys upon the Arabian horses, and they would produce it." He said: "Only those who do not know do that."