12 – As for stipulations: in this ḥadith the Prophet ﷺ stated that “Muslims are bound by their stipulations, except for any stipulation that makes lawful what Allah has forbidden or forbids what He has made lawful.” This is one of the major principles governing transactions, treaties, and contracts, for a stipulation (sharṭ) is something one contracting party requires of the other for a benefit he seeks. Whenever the two parties agree to such a term, it is permissible and binding.
13 – Thus, if a purchaser requires a specific quality in the item being sold—such as that a cow be in milk, a bird of prey be trained to hunt, or a riding animal be smooth-gaited—then the condition, being a sought-after attribute, is valid, enforceable, and obligatory.
14 – Likewise, a buyer may stipulate that the whole or part of the price be deferred to a fixed date, or a seller may stipulate a known benefit in lieu of part of the price—for example, that he continue to live in the house sold for one year, or that he use the car sold for a specified period for a defined task. All such stipulations are lawful.
15 – The same applies to the conditions set by the founders of companies or projects: provided the terms are clear, equitable, devoid of ambiguity, injustice, or excessive risk, they are binding.
16 – The conditions laid down by donors or testators regarding their endowments and bequests—so long as they are specific, purposeful, and beneficial to them—are likewise sound and compulsory.
17 – Included as well are the conditions a wife may place upon her husband: that she remain in her own house or town, that she receive a fixed allowance, or that she retain custody of her children from a previous marriage. Al-Bukhārī and Muslim record from ʿUqbah ibn ʿĀmir ﵁ that the Prophet ﷺ said, “The conditions most worthy of fulfillment are those by which marital relations have been made lawful.”
18 – Prohibited stipulations, however, include a woman’s demand that her co-wife be divorced; this is forbidden because the Prophet ﷺ said, “A woman must not ask for her sister’s divorce so as to overturn what is in her vessel” (agreed upon). A more detailed discussion will follow, God willing, in the chapter on marriage.