Is it permissible to sell wheat for flour (*Daqiq*)?
Chapter on Riba (Usury) and Exchange (Sarf)
Al-Mughni
Book of Sales
Primary text
The correct position is that selling wheat for flour is impermissible. This is the established doctrine of Sa'id ibn al-Musayyab, Al-Hasan, Al-Hakam, Hammad, Al-Thawri, Abu Hanifa, and Mak'hul, and it is the famous view attributed to Al-Shafi'i. The prohibition stems from selling wheat for its own kind unequally because grinding breaks down its particles, resulting in less volume for the same quantity by measure. If equality is not confirmed, the lack of knowledge about equality is treated as certainty of inequality in matters requiring exact equality. Furthermore, equality by weight does not necessitate equality by measure, and since both wheat and flour are items typically measured by volume (*makil*), the default rule of measure applies.
Supporting text
Another narration from Ahmad permits the sale, a view held by Rabi'ah, Malik, Al-Nakha'i, Qatadah, Ibn Shubrumah, Ishaq, and Abu Thawr. Their justification is that flour is the essence of wheat, merely broken into smaller parts, making the exchange valid like selling broken wheat for whole wheat. If this view is adopted, the exchange must be by weight to account for the diffusion of the particles during grinding, which causes flour to occupy more space by measure than whole wheat, as supported by Ishaq.