What is the ruling on a condition attached to a sale where the payment must be used to discharge a pre-existing debt to the seller?
Chapter on Selling Assets and Fruits
Al-Mughni
Book of Sales
Primary text
If a man tells his creditor, 'Sell this to me on the condition that I settle your debt with it,' and the sale is executed, the condition is void. This is because the condition restricts the buyer's ability to dispose of the item except by paying the debt. Whether the sale itself is void depends on differing narrations regarding whether void conditions invalidate a sale.
Supporting text
If the creditor stipulates, 'Settle my right from you on the condition that I sell you such and such,' the condition is void, but the settlement (payment) is valid because he has received his right. If he stipulates, 'Settle my right with better quality than my money, on the condition that I sell you such and such,' both the settlement and the condition are void, and he must return what he received and demand his money back.