Imam Aḥmad held that only one stipulation is permissible in a sales contract; Ishāq, Ibn al-Mundhir, and al-Awzāʿī agreed with him. If the buyer and seller combine two stipulations in the same transaction, the sale is rendered void.
Another report from Imam Aḥmad states that the sale remains valid when the stipulations grant the seller a clearly defined benefit in the item sold, or grant the purchaser a clearly defined benefit in the item sold that the seller undertakes to provide. This second report was adopted by Shaykh al-Islām Abū al-ʿAbbās Ibn Taymiyyah and his disciple Shams al-Dīn Ibn al-Qayyim. Our own teacher, the learned verifier ʿAbd al-Raḥmān b. Nāṣir al-Saʿdī—may Allah have mercy on them all and on the Muslims—supported and reinforced it. It is likewise the view I believe to be correct, as will become clear when we present the proofs and lines of reasoning of the scholars, may Allah Most High have mercy on them.
Proofs advanced by the preceding schools:
The three Imams based their position on the report narrated by the Five compilers from Jābir that the Prophet ﷺ “forbade the thunyā unless its extent is specified,” and on the ḥadīth transmitted by al-Tirmidhī—who declared it sound—together with al-Nasāʾī and Ibn Mājah, from ʿAmr b. Shuʿayb, from his father, from his grandfather: “Two stipulations in one sale are not permissible.” Abū Ḥanīfah likewise related that the Prophet ﷺ “forbade a sale accompanied by a stipulation.” They explained the two stipulations, and the single stipulation in the other narration, as conditions of the type under discussion—those the seller or buyer imposes on the other for some advantage tied to the commodity or for a benefit to the seller. Examples include requiring the garment to be stitched or tailored, obliging the buyer to chop or transport firewood, or reserving a specific, known benefit in the item for the seller, such as residence in the house that has been sold or the right to ride the animal for a set journey.
They answered the ḥadīth of Jābir under consideration by saying that the transaction was not a genuine sale; rather, the Prophet ﷺ only wished to benefit Jābir through a gift and used the sale of the camel as a means to that end. Their proof is the Prophet’s statement: “Do you think I bargained with you to take your camel?” Some of them added that the variation in the wordings reported in Jābir’s narration prevents it from being used as evidence for this issue. One version says, “I sold it to him on condition that he carry me to my family,” another, “The Prophet ﷺ loaned me its back until we reached Madinah,” and yet another: “I sold the Prophet ﷺ a camel and he let me ride it to Madinah.” The verb afqara means to lend the animal’s back.
As for the proofs put forward by those who allow the seller to reserve a clearly defined benefit in the item, or the buyer to stipulate a clearly defined benefit to the item that the seller must provide, they are many.