As for the domestic donkey, it is forbidden to eat and impure, as stated in the hadith of Anas, may Allah be pleased with him: the Prophet, peace and blessings be upon him, instructed Abu Talhah, may Allah be pleased with him, to proclaim on the day of Khaybar: “Allah and His Messenger forbid you the flesh of domestic donkeys, for it is filth—or impure.” (1)

His statement, “and the mule born from it is impure,” means: from the domestic donkey. A mule is an animal born when a donkey mates with a mare.

The reason for this ruling is to give precedence to the prohibitive side, because this mule is produced from a horse and a domestic donkey in a manner by which one cannot be distinguished from the other. Thus, the unlawful cannot be avoided except by also avoiding what is lawful.

If it is born from a wild donkey—as when a wild donkey mates with a mare—then this mule is pure, because the wild donkey is pure, the horse is pure, and whatever is born from two pure animals is pure.

Since these animals are impure, their leftovers—that is, what remains of their food and drink—are impure. Thus, if a domestic donkey drinks from a vessel and some water remains after it has drunk, then it is impure according to the author’s view.

Many scholars hold that the leftovers of these animals are pure if they are among those that frequently move about among us. (2)