Musnad Ahmad 5:789

Abu Sa’id narrated to us, ‘Abdullah ibn Lahi’ah narrated to us, Yazid ibn Abi Habib narrated to us, from Abu al-Khayr, from ‘Abdullah ibn Zurayr, from ‘Ali ibn Abi Talib, may Allah be pleased with him, who said: A mule was gifted to the Prophet, may Allah bless him and grant him peace, and he rode it. Some of his companions said, "If only we were to acquire the likes of this." He said, "Do you wish to mount donkeys upon horses? Only those who do not know do that."