He based this on the report of Umar ibn al-Khattāb, when he spoke to Abd Allah ibn Masūd.

Indeed, Ahmad expressly stated in more than one place that if the owner wished to sell her, his only option was to return her to the original seller at the original price, as a corresponding counter-transaction. Most of Ahmad’s later followers, however, held that this condition was invalid. They sometimes interpreted his statement, “It is valid,” to mean that the contract was valid. Yet his other explicit statements make clear that he also meant the condition itself to be valid. In this, he followed the account transmitted from three Companions: Umar, Ibn Masūd, and Zaynab, the wife of Abd Allah.

The same applies to stipulating concerning property sold that the buyer must neither sell it nor give it away, or that he must take a slave woman as a concubine, and similar conditions that designate a single use for it. Thus, Umar ibn Shabba related in The Accounts of Uthmān: “Uthmān purchased a house from Suhayb and stipulated that he would establish it as an endowment for Suhayb and his descendants after him.”

The principle encompassing all of this is that ownership confers various powers of disposal. Just as there is consensus that part of the property sold may be reserved from the sale, and Ahmad and others permitted some of its benefits to be reserved, he likewise permitted some powers of disposal to be excluded.

Accordingly, anyone who says, “This condition contradicts what the contract entails,” should be asked: Does it contradict what an unrestricted contract entails, or does it contradict what a contract necessarily entails in all circumstances? If he means the former, then every condition does so. If he means the latter, his claim is not conceded. What is prohibited is a condition that contradicts the purpose of the contract, such as stipulating divorce in a marriage or stipulating the dissolution of a contract. If, however, a person stipulates something that is itself sought through the contract, it does not contradict the contract’s purpose.

This position is correct, as demonstrated by the Quran, the sunnah, consensus, and sound reasoning, together with the presumption of continuity and the absence of any contrary evidence.

As for the Quran, Allah Most High says: “O you who believe, fulfil your contracts.” [al-Mā'ida: 1]