Is the exchange (Sarf) valid if one exchanges a debt owed as a deposit (Wadi'ah) with another person?
Chapter on Riba (Usury) and Exchange (Sarf)
Al-Mughni
Book of Sales
Primary text
The exchange (Sarf) is valid if the existence of the deposited Dinars is known or presumed to remain. The validity is established because the transaction is considered permissible based on the known or presumed existence of the underlying asset.
Supporting text
If one presumes the deposited amount is non-existent, the exchange is invalid because its legal status is that of a non-existent item. If there is doubt regarding its existence, Ibn Aqil and some Shafi'is permit the exchange based on the principle that the default assumption is its continued existence, as doubt does not negate certainty. Conversely, Al-Qadi and Imam Al-Shafi'i state it is invalid because its continued existence is not known for certain.