Musannaf Ibn Abi Shaybah

It is narrated from Hazrat Ali (may Allah be pleased with him) that the Messenger of Allah (peace be upon him) was gifted a white mule. I said, "If we wished, we could have done the same (i.e., produced a white mule)." He (may Allah be pleased with him) asked, "How?" We replied, "By mating a donkey with an Arabian horse, such offspring are produced." The Prophet (peace be upon him) said, "Such an act is done by one who is ignorant."

It is also narrated in a similar manner from Hazrat Aamir (may Allah be pleased with him).

Hazrat Yazid (may Allah be pleased with him) narrates that Hazrat Umar bin Abdul Aziz wrote to us, and his letter was read out to us. In it was written that whoever mates a donkey with an Arabian horse, deduct ten dinars from his grant (gift and stipend).

It is narrated from Hazrat Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) forbade mating a donkey with a horse.

It is also narrated in a similar manner from Hazrat Ali (may Allah be pleased with him).

Hazrat Dihyah al-Kalbi (may Allah be pleased with him) submitted, "O Messenger of Allah (peace and blessings be upon him)! Should we not mate a donkey with a horse so that a mule is produced on which we may ride?" The Prophet (peace and blessings be upon him) said: "This is done by one who is ignorant."