Musannaf Ibn Abi Shayba 28:658

Yazid ibn Harun narrated to us, he said: Amr ibn Maymun informed us, he said: [A man] from the Banu al-Harith, who was in charge of the frontier of Malatya, wrote to Umar ibn Abd al-Aziz: "Indeed, men go on military expeditions with weak horses, whether they are *jadha'* (young) or *thani* (older), and there is no defense in them for the Muslims. And a man goes on an expedition with a strong *bardhun* (pack horse/non-Arab horse) which is not inferior to an Arabian horse, except that it is called a *bardhun*. So what is the opinion of the Commander of the Faithful regarding them?" Umar ibn Abd al-Aziz wrote back to him: "Look at those weak horses which provide no defense for the Muslims, and inform their owners that you will not grant them a share (of the spoils) whether they take them along or leave them behind. As for those *baradhin* (non-Arab horses) which are impressive in their running and appearance, grant them a share just as you grant a share to the Arabian horses."