Glossary
Ribawi commodity
Definition
One of the six commodities specified in hadith as subject to special exchange rules: gold, silver, wheat, barley, dates, and salt.
Exchanges of the same ribawi commodity must be equal in quantity and hand-to-hand. Exchanges of different ribawi commodities of the same category (e.g., gold for silver) require hand-to-hand settlement but allow unequal quantities.
Most scholars extend the rule by analogy (qiyas) to anything used as money (currencies) and to staple foods. This is why spot gold trading must settle immediately and forex must be hand-to-hand.