Hastings' Dictionary of the Bible (1898)
MULE, the name of the offspring of the horse and the ass. 2 Sam 13:29. It is smaller than the former, and is a remarkably hardy, patient, obstinate, sure-footed animal, living ordinarily twice as long as a horse. Mules are much used in Spain and South America for transporting goods across the mountains. So also in the Alps they are used by travellers among the mountains where a horse would hardly be able to pass with safety. In the United States mules are much used for draught. Even the kings and most distinguished nobles of the Jews were accustomed to ride upon mules.
See passage above cited, and also 2 Sam 18:9; 1 Kgs 1:33; 1 Kgs 10:25; 1 Kgs 18:5; 2 Chr 9:24; Esth 8:10, 2 Kgs 22:14. It is probable that the Jews purchased, but did not raise, mules. Lev 19:19.