such as iron, brass, copper, potash, and the like. Anything that is neither measured nor weighed does not come under the ruling, even when edible, like individually counted fruits.
They support this line of reasoning with the report transmitted by Ahmad from Ibn ʿUmar in which the Messenger of Allah ﷺ said, “Do not sell one dīnār for two dīnārs, one dirham for two dirhams, or one ṣāʿ for two ṣāʿs.”
They also cite what al-Dāraqutnī narrated from Anas: the Prophet ﷺ said, “Whatever is weighed must be like for like when it is of one and the same kind, and whatever is measured, likewise; but if the two kinds differ, there is no harm.” In this ḥadith the requirement of equality is clearly linked to weight or measure within a single genus, which establishes their operative cause.
Al-Shāfiʿī held that the cause with the four foodstuffs is their being edible and of the same genus, whereas with gold and silver it is their function as a price for goods, so the ruling is confined to those two metals. His evidence is the ḥadith recorded by Muslim from Maʿmar ibn ʿAbd Allāh: the Prophet ﷺ “forbade selling food for food except like for like.” Because the ruling is attached to the word “food,” the effective cause is derived from it.
Imām Mālik concurred with al-Shāfiʿī regarding the two monetary metals. As for the others, he traced the operative cause to genus, storability, and suitability as a staple, as well as to whatever seasons food, such as spices. He maintained that the four items mentioned in the ḥadith were cited to alert us to everything that shares their meaning, and what unites them all is that they are stored staples.
Thus wheat and barley stand for all grains; dates represent all sweeteners such as sugar and honey; and salt represents the various spices.
Another report from Imām Aḥmad—also the earlier view of al-Shāfiʿī and the opinion of Saʿīd ibn al-Musayyib—holds that the operative cause in the four specified items is edibility combined with being sold by measure or weight. Consequently, ribā does not apply to an edible that is neither measured nor weighed, such as pomegranates, fresh herbs, or melons, nor does it apply to anything measured or weighed that is not edible. Both elements must be present: measure or weight alone does not necessitate equality, and edibility alone cannot realise equality because there is no legal yardstick for it. True equivalence is only established by the sharʿī standard, namely measure and weight.