Is it permissible to exchange flour (Daqiq) for parched barley flour (Suwayq)?
Chapter on Riba (Usury) and Exchange (Sarf)
Al-Mughni
Book of Sales
Primary text
The correct ruling is that exchanging flour for parched barley flour is not permissible. The supporting evidence for this prohibition is that fire has affected one of the commodities (the Suwayq), thereby invalidating an exchange between them, similar to exchanging roasted grain for unroasted grain.
Supporting text
A narration from Ahmad permits this exchange because both commodities are parts of wheat that exist independently, making the exchange between them similar to exchanging flour for flour or parched barley flour for parched barley flour. Another view, narrated from Malik, Abu Yusuf, Muhammad, and Abu Thur, permits an unequal exchange (tafādul) between flour and parched barley flour because they are considered two distinct genres (jinsayn). However, the primary ruling is that since they are parts of a single genre (wheat), an unequal exchange between them is prohibited, similar to flour exchanged for flour.