He was asked:

A man is owed one hundred and eighty by another man. Someone said to him, “Will you sell it for one hundred and fifty?” Is that permissible?

He replied:

All praise is due to Allah. If the debt is payable at a future date and he sells it for a smaller amount payable immediately, this is usury. But if it is already due and he takes part of it and releases the debtor from the remainder, his reward rests with Allah, and he has done good.

He was asked:

A debt arising from a salam sale—payment in advance for later delivery—has fallen due, but the recipient of the advance payment does not have the means to fulfil it. He says, “Sell it to me for more than the original price.”

He replied:

It is not permissible to sell a debt arising from a salam sale before taking possession of what is owed, nor to sell a debt for a debt. Thus, this is forbidden on two grounds.

There is also a third ground: if he sold him dirhams for dirhams, as in the case of someone who makes a usurious sale on deferred terms, he may not accept a substitute for its price