What is the ruling on exchanging different types of staple food commodities (e.g., wheat for barley)?
Chapter on Riba (Usury) and Exchange (Sarf)
Al-Mughni
Book of Sales
Primary text
The ruling is that exchanging different staple food commodities, such as wheat for barley, is permissible when done hand-to-hand (yadan bi-yadin), but not permissible on credit (nasi'ah). This is established by the explicit and sound Hadith of the Prophet (peace be upon him): 'Sell barley for wheat however you wish, hand to hand.' Furthermore, another narration states, 'There is no issue with selling wheat for barley... if these categories differ, sell however you wish.' This explicit evidence supersedes other considerations.
Supporting text
A dissenting view, based on the report concerning Ma'mar ibn 'Abdullah, suggests that all staple foods must be exchanged in exact measure for measure (mithlan bi-mithl) because the Prophet (peace be upon him) forbade the exchange of food for food except measure for measure. This view is rebutted by citing the specific permission regarding wheat and barley, arguing that Ma'mar's incident required an implicit understanding of the specific commodity or that his action and statement cannot supersede clear Prophetic command. Furthermore, the analogy used by this dissenting group breaks down when considering gold and silver.