Accordingly, every item that shares with these six explicitly named commodities the very same effective cause—whether it is an edible sold by measure, an edible sold by weight, or, in the case of currencies, it possesses the attribute of serving as a medium of exchange—falls under the ruling of riba. When, in addition to the cause, the genus is also one and the same—for instance, wheat for wheat—both surplus and deferred delivery are forbidden, for the Prophet ﷺ said: “Gold for gold, silver for silver, wheat for wheat, barley for barley, dates for dates, and salt for salt—equal for equal, hand to hand.” Narrated by Muslim and Abū Dāwūd.

The phrase “hand to hand” means that the exchange must be completed on the spot, with each party taking possession in the same gathering before they separate. If both the cause and the genus differ, however, then both excess and deferment are permissible, such as gold for wheat or silver for barley.

Furthermore, one must know that a commodity sold by measure may not be exchanged for the same commodity except by measure, and a commodity sold by weight may not be exchanged for the same commodity except by weight. The Prophet ﷺ said: “Gold for gold—weight for weight; silver for silver—weight for weight; wheat for wheat—measure for measure; barley for barley—measure for measure.” Any transaction that departs from its prescribed standard prevents the certainty of equality; therefore it is impermissible to sell a measured commodity