Q .A deal was concluded between two people at a given price. However, both parties agreed that the buyer should pay an extra amount over the specified price if he wrote a post-dated check. Is this permissible?
A: If the deal was concluded at a given price and the extra amount was for the delayed payment to settle the original amount, such an increase is ribā which is unlawful. Nor can it be ḥalāl because the parties agreed to it.