Muhammad ibn Harun,brother of the gifted poet and writer Sahl ibn Harun, rode a mule that bolted underneath him in a fit of fright. This happened in broad daylight, in the quadrangle by the Gate of ‘Uthman [ibn Abi 'l-‘As, in Basra]. They say that in the commotion, Muhammad's abdomen was lacerated by a saddle-strap, and that he died on the animal's back—and that his mule collided with another, killing both animals together with their riders.
It was reported to me by Sa‘id ibn Abi Malik that a stablehand belonging to one of the land grant holders [of Rabi‘ ibn Yunus, in Basra] used to copulate with his master's she-mule. One day, while he was in the act, the mule retreated backward to increase the his thrusting power, until he was pressed into a corner of the stable where he was crushed to death. Another servant came to the stable on some errand and, finding it barred from inside, called out his fellow's name. Hearing no answer, he wrenched open the door to find his body squashed into the corner, with the mule pressing back against him still. At his cry, the mule stepped away, and the servant fell down dead.
Some have opined that, even though the active role in their coupling was played by the stablehand, the true aggressor was the mule, who used to lick her lips every time she saw him, and no one else. If assault wasn't her intent, then he was killed in retribution or self defense.
These verses are from a satire by Qays ibn Yazid, in which he accused Ibn Abi Sabra of fornicating with his own mule (meter: kāmil):
They tell me the mule you dote on
gets restless when you don't screw her.
She lowers her rump and swings it toward you
when she sees you coming over the wall of the manger
They say that when the poet al-Farazdaq was captured by a group of Banu Kulayb, they brought a she-ass and said, "Either fornicate with this animal, as you accused ‘Atiyya ibn al-Khatafi [father to the poet Jarīr] of doing, or we kill you." Al-Farazdaq said, "In that case, bring me the rock ‘Atiyya stood on when he shtupped her, so I can accomplish the same." They all laughed at his wit, and let him go.
Another man killed by mules was Zayd ibn Hulq, whose job it was to train them. His sons are famous at Basra. Also killed by mules were Muhammad ibn Sa‘id ibn Hazim al-Mazini and his uncle, ‘Amr ibn Haddab, killed by a mule at Shushtar. And al-Muhallab ibn Abi Sufra died on muleback at al-Talaqan. Iyas ibn Hubayra al-‘Abshami, who once paid bloodwit, also died on the back of a mule, a mean one.
From The Book of Mules by al-Jahiz