that they are not the buyer’s property, then—according to the view that they are specified by designation—the contract is invalid.
If it is defective with something of the same type, he may retain it or return it.
His statement, “If it is defective with something of the same type, he may retain it or return it,” means that he may retain it without compensation for the defect, or return it.
For example, someone buys a dinar for a dinar and then finds that the dinar is defective with something of the same type; that is, it has been mixed with inferior gold. The sale is a dinar for a dinar, and when a dinar is sold for a dinar, equality is stipulated. This man finds that the dinar he specified is defective with something of the same type. What do we say to him? We say: he now has the choice. If he wishes, he may retain it without compensation for the defect; and if he wishes, he may return it.
That he may return it is clear, since it is defective, whereas he only purchased something sound. As for retaining it without compensation for the defect, this is because such compensation would entail an increase in the sale of one type for the same type. As is known from the principles previously mentioned, when one type is exchanged for the same type, equivalence is stipulated. Hence he said, “He may retain it,” meaning without compensation for the defect, “or return it.”
It is understood from the author’s words—may Allah have mercy on him—“with something of the same type,” that if the defect is from a different type, the contract is invalid. Thus, if he finds it defective with something of a different type, we say: there is no option here; rather, the contract is void.
For example, if he sells a dirham for a dirham and finds that one of the two dirhams is defective because of copper, the contract is void, since the defect is from a different type. It is then akin to the case of a mudd of Ajwa dates and a dirham, because he has exchanged one type for the same type while one side includes something of a different type; thus, it is invalid.
All of this is based on the view that dinars and dirhams become specified through designation