It is narrated from Hazrat Dihyah Kalbi (may Allah be pleased with him) that once I submitted in the presence of the Messenger of Allah, "O Messenger of Allah! Should I not do this: let me mount a donkey on a horse (let them mate), so that a mule is produced and you may ride on it?" The Noble Prophet (peace and blessings be upon him) said, "This is done by those people who do not know anything."