it varies, and it has no fixed standard, so it would be unknown. If they agree that he rides for three days and [walks for three days], or more or less, it is permissible. If they disagree, neither of the refraining parties shall be compelled; because there is harm in it for each of them: for the walker due to the continuity of walking, and for the camel due to the continuity of being ridden; and because when he rides after the intensity of his fatigue, it is heavier on the camel. If two people hire a camel to ride it by alternating turns, it is permissible, and their lease shall be for the duration of the journey, with the fulfillment of the turns between them according to what they agree upon. If they are contentious, it shall be divided between them, with each of them having known farsakhs, or one of them having the night and the other the day. If there is a custom for that, it is referred to it. If they disagree on who starts, they shall draw lots. It is also possible that their lease is not valid unless they agree on a known ride for each of them; because it is a contract on an unknown matter with respect to each of them, so it is not valid, just as if they had purchased two slaves with the condition that each of them receives a specific slave of the two.

908 - Issue: He said: (If he sees the riders, or they are described to him, and the remainder is mentioned with known weight units, it is permissible.)

In summary, knowledge through description serves as a substitute for seeing the riders when they are described in terms of what they differ in—such as height and shortness, leanness and fatness, health and illness, youth and age, and being male or female—and for the remainder, it suffices to mention the weight. Al-Sharif Abu Ja'far and Abu al-Khattab said: It is essential to know the riders by sight; because it varies by his weight and lightness, and his stillness and movement, and it cannot be strictly controlled by description, so it must be specified. This is the school of al-Shafi‘i. Regarding the camel litter (mahmil), they have a view that description is insufficient and it must be specified. Our view is that it is a contract of exchange related to an animal, so description suffices for it, like a sale and like the mount in a lease, and because