Musannaf Ibn Abi Shaybah 35394 — The horseman: how much is he

Amr bin Maymun (may Allah have mercy on him) said that Umar bin Abd al-Aziz wrote to the people of al-Jazirah: To proceed: in the blessed era of the Messenger of Allah (peace and blessings be upon him), two shares were fixed for the horse and one for the rider. I did not think that anyone would set out to reduce any obligatory share of it, until men among those who fight at these fortresses did so. So return to them the shares that were theirs in the era of the Messenger of Allah (peace and blessings be upon him), and those shares were that two were fixed for the horse and one for its rider. How can you reduce the share of the horse, when by Allah's permission horses roam in the pasture at night, are assigned to guarding the frontiers by day, and also seek what the fighters seek?