prohibiting unequal exchanges of these commodities to be their character as food alone. As for Abū Hanīfa and his followers, they extended the ruling for wheat, barley, dates, and salt by analogy to everything measured by volume, whether food or other goods, since all these share measurement by volume, which he regarded as the legal cause for prohibiting unequal exchanges. They likewise extended the ruling for gold and silver by analogy to everything weighed, whether food or other goods, since all these share measurement by weight, which he regarded as the legal cause for prohibiting unequal exchanges.
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Drawing an analogy with gold and silver is not valid, because there is consensus that anything measured by volume or weight may be purchased with gold or silver, whether hand to hand or on deferred terms. Thus, anyone who draws an analogy between gold and silver and such weighed commodities as iron and lead—just as he draws an analogy between foods measured by volume and wheat, barley, dates, and salt—would have to prohibit purchasing iron and lead with gold or silver on deferred terms, just as he prohibits purchasing chickpeas and lentils with wheat and barley on deferred terms. Yet there is consensus that the former is permissible. Saʿīd ibn al-Musayyab extended the ruling for the wheat, barley, dates, and salt mentioned in the hadith by analogy specifically to foods measured by volume or weight. Dāwūd and the literalists departed from the prevailing view, holding that ribā applied only to the four commodities expressly named by the Prophet, may Allah bless him and grant him peace. To support permitting unequal exchanges of anything else, they invoked the general wording of Allah’s statement—exalted and majestic is He:
“Allah has permitted trade and forbidden ribā.” [al-Baqara: 275]
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According to Mālik and his followers—may Allah Most High be pleased with them—food falls into four categories: food that is stored and used as a staple or to season staple foods, and ordinarily forms a basic source of sustenance; food that is stored and used as a staple or to season staple foods, but does not ordinarily form a basic source of sustenance; food that is only rarely stored; and food that is not stored at all. As for food that is stored and used as a staple or to season staple foods, and ordinarily forms a basic source of sustenance, unequal exchanges within a single kind are prohibited by agreement within the school. As for food that is stored and used as a staple but does not ordinarily form a basic source of sustenance, such as walnuts, almonds, and hazelnuts