مسند أحمد

It was narrated that ‘Ali (رضي الله عنه) said: A male or female mule was given to the Messenger of Allah (ﷺ) as a gift. I said: What is this? He said: `A mule.` I said: Where does it come from? He said: `From mating a male donkey with a mare, and this is what is produced.` I said: Should we mate [a donkey] with [a mare]? He said: `No, this is only done by those who do not know.”