And His statement: “The Muslims are bound by their conditions, except a condition that makes lawful what is unlawful or makes unlawful what is lawful.” (1)

As for the specific evidence, it is that the Prophet purchased a camel from Jabir ibn Abdullah, stipulating that Jabir be allowed to ride it to Medina, and the Prophet agreed to this. (2) This is a known benefit attached to the item sold, and is therefore like residing in the house for one month.

His statement, “residence in the house for one month,” indicates that if he stipulates residence in a house other than the one being sold, the condition is invalid. Thus, if he says, “I have sold you this house for one hundred thousand dirhams on condition that you accommodate me in your house for one month,” then, according to the author, neither the sale nor the condition is valid. This is based on what will follow: that making the condition of one contract within another contract invalidates the contract. Thus, it must concern the very item over which the contract was concluded. If it concerns something else, it combines a sale and a lease, which is invalid.

His statement, “that the camel be ridden to a specified place,” specifies the benefit by place, whereas the earlier phrase, “residence in the house for one month,” specifies it by time.

An example is that he says: “I have sold you this camel on condition that I travel upon it to Mecca and return.” The sale is valid, and the condition is valid.

Another example: “I have sold you this car for fifty thousand, on condition that I perform Hajj using it and return.” Here, the sale is valid and the condition is valid, because it is a known benefit attached to the item sold.