His statement, “Among them are invalid conditions that invalidate the contract,” means: and there are invalid conditions that do not invalidate the contract, which the author will mention later, if Allah Most High wills.

His statement, “such as either party stipulating upon the other another contract, such as an advance-payment sale,” refers to a condition that is invalid and invalidates the contract. Thus, if either party stipulates another contract upon the other, the contract is invalid. “Such as an advance-payment sale” means a salam sale: payment is made in advance while delivery of the commodity is deferred. For example, the buyer says to the seller, “Here are one hundred dirhams for one hundred sāʿs of wheat, which you will give me after one year.” Thus, if one of them sells something to the other—such as a house—and says, “On condition that you deliver to me one hundred dirhams’ worth of one hundred sāʿs of wheat,” then this condition is invalid and invalidates the contract.

If someone were to ask: Why did he separate this from what came before?

We reply: Because what came before may be valid or invalid. If he stipulates one condition, the condition is valid; but if he combines two conditions, it becomes invalid. Here, however, it is inherently invalid and admits of no such division; this is why he separated it from what came before.

His statement, “and a loan”: likewise, if he stipulates a loan. For example, he says to him, “Sell me this house of yours.” The other replies, “I will sell it to you on condition that you lend me one hundred thousand.” This condition is invalid and invalidates the contract. Thus, neither the loan nor the sale is valid.

His statement, “and a sale”: that is, if he stipulates another sale upon him. He asks him to sell him his car, and says, “I will sell it to you for fifty thousand on condition that you sell me your car for fifty thousand, or for less, or for more.” In this case, neither the original sale nor the stipulated sale is valid.