Thus, one may sell one slave from among his slaves if this does not frustrate the intended purpose. But if it does frustrate the intended purpose, specification is necessary.
A question: There is a type of sale commonly practiced today: a person has a pile of watermelons and says to you, “I sell you one from this pile for two riyals; choose whichever you wish.” The common practice today is to regard this sale as valid and binding: if the buyer takes the watermelon he wants, whether the seller approves his choice or objects, the sale stands. The seller knows that the highest possible price of any watermelon in this lot is two riyals, and he knows that he is not being cheated. Therefore, it seems that such a sale should be deemed valid, because people customarily engage in it and do not regard it as involving uncertainty or excessive risk. The basic principle regarding sales and contracts is that they are permissible and valid.
The same applies to selling one sheep from a flock. A person may come to a flock of sheep and say, “Choose whichever you wish for one hundred riyals.” This too is established by customary practice, and when the buyer chooses, the seller knows that the highest possible value is one hundred riyals.
“No exception may be made except of a specified item. If, from an animal whose meat may be eaten, he excludes its head, hide, and limbs, the sale is valid. The opposite ruling applies to its fat and its unborn young. It is valid to sell that whose edible part is inside it, such as pomegranates and watermelons; likewise, to sell broad beans and the like in their pods, and fully ripened grain in its ears….”
His statement, “No exception may be made except of a specified item,” means that it is not valid to exclude one slave from among a group of slaves unless he is specified. Thus, if he says, “I sell you these slaves except for one,” the sale is invalid because of the uncertainty.
They said: This is because uncertainty concerning what is excluded entails uncertainty concerning what remains subject to the sale. Thus, excluding an unknown item from known items renders them unknown.
For example, there are ten slaves before us. The subject of the sale is initially known, but if we exclude one of them, what is being sold becomes unknown, because that one slave may be worth half the value of the entire group. Accordingly, such an exception is invalid.