Musannaf Ibn Abi Shayba 28:1175

33703. Abd al-Rahim ibn Sulayman narrated to us, from Muhammad ibn Ishaq, from Yazid ibn Abi Habib, who said: Umar ibn Abd al-Aziz wrote to us, and his letter was read to us: "Any man who loads a donkey onto a horse-drawn carriage, erase ten dinars from his stipend."