An example of this is: I sell this car for one hundred thousand, payable in one year. This is one sale. Then I buy it back from the buyer for eighty thousand in cash; this is another sale. Which of the two prices is the lesser? Eighty thousand. The seller must either limit himself to the eighty thousand and not demand the additional twenty thousand; otherwise, if he demands the additional amount, that is usury. This is why he said: “He is entitled to the lesser of the two prices, or else it is usury.” That is, we say to the seller: You are entitled only to the eighty thousand, and you may not demand anything further from the buyer; otherwise, it is usury, for this is undoubtedly a stratagem for usury.
As for those who say that the meaning of the hadith, “He forbade two sales in one sale,” is that a person says, “I sell you this for ten in cash or twenty on deferred payment,” this is incorrect. Rather, there is nothing wrong with this, for one of two things must occur: either the parties separate without settling upon a price, or they settle upon the price before separating. If we settle upon the price before separating, and I say, “I take it for ten in cash,” then it is one sale. But if we separate, the price remains unknown; and it is well known that one of the conditions of a valid sale is that the price be known. Thus, it is prohibited in this case not because it constitutes two sales in one sale, but because the price is unknown. Therefore, if he specifies it by saying, “I sell you this for ten in cash or twenty on deferred payment, and you have the option for two days,” then this is permissible, because there is nothing objectionable in it.
Thus, two sales in one sale applies only to the case of an ʿīnah transaction, because the Prophet ﷺ said: “Whoever makes two sales in one sale is entitled to the lesser of the two prices, or else it is usury.” This does not apply to the case mentioned by the author. Accordingly, the sound view is that if one makes another contract a condition of a sale, both the condition and the sale are valid, except in two cases, as will follow.