Recurrent are the conditions set by a seller or a buyer when concluding a trade transaction. Accordingly, it has become a necessity to study and tackle the different kinds of such conditions, pointing out the legal and the illegal ones among them. The scholars of Islamic Jurisprudence, defined a condition (of a trade transaction) as follows: "It is obligating one of the two parties (of the sale) by the other for the benefit of the latter." According to them, a transactional condition is invalid unless it is made at the time of the transaction and embedded in the transactional contract. In other words, a condition is invalid if made before or after concluding the contract.

Valid conditions are those that do not contradict the objective of the contract. Such a kind of condition obligates its fulfillment; the Prophet said: "Muslims must keep to the conditions they make."  [Abu Daawood & At-Tirmithi]

2-    The second kind of valid transactional conditions is that in which one of the two parties stipulates benefiting lawfully from the commodity in a certain way. For example, a seller of a house may stipulate staying therein for a specific period, or a seller of a riding animal or a car may stipulate riding it to a certain place. Jabir, may Allah be pleased with him, narrated: "The Prophet sold a camel and stipulated to ride it (and use it) until he reaches Madeenah."  [Al-Bukhari and Muslim]

1-    The first kind is the invalid illegal condition that basically nullifies the selling contract, such as when one of the two parties stipulates another contract within the main one. For example, it is an illegal condition when a seller of a commodity makes a condition that the buyer must make him his partner in business, lend him a sum of money, or allow him to share his house, etc., or that he says, "I sell you this commodity on the condition that you rent me your home." Such a condition is legally invalid so it nullifies the original contract. This is because the Prophet forbade concluding a selling contract based on another conditional contract. (At-Tirmithi & An-Nasaa'i) This Prophetic prohibition was interpreted by Imaam Ahmad Ibn Hanbal exactly as we have pointed out above.

The phrase "in the Book of Allah" in the aforementioned Hadeeth refers to Sharee'ah (Islamic Law) including the Quran and the Sunnah. Still, such an invalid type of conditions does not nullify the contract. To illustrate, in the well-known incident of Bareerah, the one who sold her made a condition that her wala (The freed slave's loyalty by virtue of emancipation) would go to him if she was emancipated. However, the Prophet declared that the condition was null, yet he did not consider the contract to be invalid. Then, the Prophet said: "Verily, the Wala' is for the emancipator." [Al-Bukhari and Muslim]