the highest form of knowledge, and description. In description, it is a condition to know two things: the quantity and the type; because the fatigue of the animal varies according to the type, even with equality in quantity. For instance, cotton harms it in one way, which is that it expands on the animal, allowing wind to enter it, thereby becoming heavier. Something similar made of iron causes harm in [another respect], which is that it accumulates on one spot of the animal, so it may wound it, thus it must be clarified. As for containers, if they are included in the weight, there is no need to mention them. If they are not weighed and they are known containers that do not vary, such as burlap sacks for wool, hair, and the like, the contract is permissible without specifying them, because they rarely vary significantly, so naming them is sufficient. If they do vary, they must be known by specification or description. Ibn Aqil mentioned that if he says, "I have leased it to you so that you may carry on it three hundred ratls of whatever you wish," it is permissible, and he possesses that right. However, he must not load it with a load that harms the animal; for example, if he wishes to carry iron or mercury, he ought to distribute it across the animal's back so that it does not gather in one place on its back, nor should he place it in a container that shifts about, causing the animal distress and fatigue. If he leased a back [of an animal] for carrying, described by a specific type, and he wishes to carry it on a type other than that, and the one requesting that is the lessee, it is not accepted from him, because he does not have the right to demand what he did not contract for. If the lessor requests it, and it would cause a purpose of the lessee to be lost—such as if his purpose was to hasten the travel, or so as not to be cut off from the caravan, so horses or mules are determined; or if his purpose was the stability of the load because the load is of a type that is harmed by shaking, or its strength and endurance for the length of the journey and the heaviness of the load, so he determines camels—it is not permissible to deviate from it, because it causes the loss of the lessee's purpose, so that is not permitted, just as it is in the case of a mount. If it does not cause the loss of a purpose, it is permissible, just as it is permissible for one who leased [an animal] to carry something to carry something similar to it, or something less harmful than it.