Is it valid to use a pre-existing debt (dayn) as the capital (thalb al-salam) for a forward sale (salam) in food?
Chapter on Guaranteed Salaf (Advance Payment) for a Specified Term
Al-Mughni
Book of Sales
Primary text
This transaction is invalid. Scholars who agree on this ruling include Ibn al-Mundhir, Malik, al-Awza'i, al-Thawri, Ahmad, Ishaq, the Companions of Opinion (Ahl al-Ra'y), and al-Shafi'i. Ibn 'Umar stated that this is not permissible. The rationale is that since the commodity being sold forward (al-muslam fih) is a debt, making the price also a debt constitutes a sale of debt for debt (bay' dayn bi-dayn), which is invalid by consensus.