—are subject to ribā by unanimous agreement, for an authentic and unequivocal text exists concerning them. The scholars then differed about everything else: does ribā apply to other items or not?

The Ẓāhirīs restricted ribā to these six categories alone and did not extend it to anything beyond them, because they negate analogical reasoning (qiyās).

The majority of scholars, who uphold qiyās, did extend the ruling to other commodities. They nevertheless disagreed over which things should be attached to the original six, and that difference follows their disagreement over the ʿillah (effective cause) of ribā.

Those who held that the ʿillah is measurement by volume or by weight maintained that ribā applies to everything that is customarily measured or weighed, even if it is not edible.

Those who stipulated, in addition to volume or weight, the quality of being edible, confined ribā to things that are both measured (by volume or weight) and eaten.

The stronger view is that the ʿillah of ribā extends beyond the six items expressly named. As for the two monetary metals, their ʿillah is thamaniyyah—their function as a medium of exchange—so whatever is prepared to serve as money, of whatever substance, shares that ʿillah.

Regarding the remaining four items, the ʿillah is the conjunction of edibility with either measurement by volume or by weight. Anything measured or weighed that is not eaten is outside the scope of ribā, and anything edible that is neither measured nor weighed is likewise outside it. But once edibility coincides with either weight or volume, the ʿillah of ribā is present.

Weight and measure are mentioned in the hadith of Anas recorded by al-Dāraqutnī (3/18), in which the Prophet (peace and blessings be upon him) said: “Whatever is sold by weight must be like for like, and whatever is sold by measure must likewise be like for like; but if the two kinds differ, there is no harm.” Edibility appears in the report narrated by Muslim (1592) from Maʿmar ibn ʿAbd Allah: “The Messenger of Allah forbade the sale of foodstuff except like for like.”

By adopting this view, all the evidences on the issue are brought into harmony, and each hadith is duly qualified