A mule was gifted to the Messenger of Allah ﷺ, and he rode it.Ali said, "If we were to breed donkeys with horses, we would have mules like this one."The Messenger of Allah ﷺ replied, "Only those who do not know do such a thing."
أهديت لرسول الله ﷺ بغلة فركبها، فقال علي: لو حملنا الحمير على الخيل فكانت لنا مثل هذه، قال رسول الله ﷺ: إنما يفعل ذلك الذين لا يعلمون.
This was narrated by Abu Dawud (2565), Nasai (3580), and Ahmad (785), and Ibn Hibban (4682) and Bayhaqi (10/22) graded it sahih, all of them through the route of Layth, from Yazid bin Abu Habib, from Abu Khayr (that is, Marthad bin Abdullah), from Abdullah bin Zurayr, from Ali bin Abu Talib, who narrated it. Its isnad is sahih. Nawawi also graded it sahih in Majmu (6/178). It has other routes as well, but the one I have mentioned is the most sahih of them.Khattabi said in Maalim Sunan (2/251), "It seems that the meaning in this, and Allah knows best, is that when donkeys are bred with horses, the benefits of horses are lost, their numbers decrease, and their growth is cut off. Horses are needed for riding, galloping, and pursuit, and with them the enemy is fought, and with them spoils are secured. Their meat is also eaten, and a share is allotted for the horse just as a share is allotted for the rider. The mule has none of these virtues. So ﷺ wished for the number of horses to grow and their offspring to increase, because of the benefit and good found in them."