Donkey's, like most animals, come from other donkeys however they have been known for interbreeding. Horse/donkey hybrids are popular for their durability and vigor. A mule is the offspring of a jack (male) donkey and a mare (female horse). The mating of a male horse and a female donkey produces a hinny. Most of these offsprings are almost always sterile.
https://en.wikipedia.org/wiki/Donkey