—in the incident of Barīrah the Prophet ﷺ said, “Any condition that is not found in the Book of Allah is null and void.” Therefore, every stipulation that has no foundation in the Qur’an or in the consensus is rejected.

Their second proof is analogy: they treat every condition that contradicts the purport of a contract as analogous to the invalid stipulation concerning walāʾ, because the effective cause in all such cases is that the term runs counter to what the contract, by law, necessarily entails. To alter those entailments is therefore to alter what the Law itself has imposed, much as changing the prescribed acts of worship would be. This is the crux of the principle: contracts have been legislated in a specific form, so inserting a term that conflicts with that form is an alteration of what the Law has instituted.

The second position is that the basic rule governing contracts and conditions is permissibility and validity; nothing is prohibited or rendered void unless the Sacred Law, by explicit text or by sound analogy, declares it so. Most of the explicit statements transmitted from Imam Aḥmad proceed on this principle, and Mālik’s approach is close to it, though Aḥmad is readier than Mālik to validate conditions. Whenever Aḥmad upholds a contract or a condition, he does so on the strength of a particular proof—either a reported precedent or a compelling analogy—and he is not deterred merely because the term appears to conflict with the contract’s purport or lacks an explicit text. In this regard he had access to reports from the Prophet ﷺ and the Companions that other imams did not.

Both Qur’an and Sunnah command the fulfillment of covenants, undertakings, conditions, and contracts, the rendering of trusts, and the safeguarding of them. Since honoring one’s word and keeping covenants is commanded in principle, it follows that the default is that contracts and conditions are sound; for “soundness” has no meaning except that their legal effects follow and their intended purposes are realized—and the purpose of a contract is its fulfillment. Abū Dāwūd relates from Abū Hurayrah that the Messenger of Allah ﷺ said, “Reconciliation is permissible among Muslims except for a settlement that makes lawful what is unlawful or makes unlawful what is lawful; and the Muslims are bound by their conditions.” Al-Tirmidhī graded this ḥadīth as sound and authentic.

This is precisely what the Book and the Sunnah attest to, and it is the true tenor of the madhhab. Through a condition, the stipulator seeks to make obligatory something that, without the condition, would not have been obligatory. The very point of conditions is to create an obligation where none previously existed and that is not itself forbidden. Thus, whatever was merely permissible without the term becomes obligatory by virtue of it. The sound, consistent analogy on this question—the one on which the principles of Aḥmad and other jurists of ḥadīth rest—is that stipulating an increase beyond an unrestricted engagement, or stipulating a reduction, is permissible so long as the Law sets no barrier against it.