Is it permissible to keep a sum of money that was taken as settlement for a debt owed by the deceased, knowing that the principal amount of the debt was later returned, and that the heirs are demanding the return of the larger sum due to the difference in exchange rates?

If a deceased person owes dues to others, the heirs must disburse them before dividing the inheritance, based on the verse: (from after a will is executed or a debt is paid), and the Hadith: "The soul of a believer remains suspended by his debt until it is paid off." So, if the deceased acknowledged an amount to the claimant, the heirs must promptly pay it from the estate. It is not permissible for the claimant to take the son's money in exchange for his father's debt. The amount must be returned to its owner in the same currency. As for the additional profits claimed by the creditor from the deceased, if the deceased did not acknowledge them, the claimant must provide evidence for them. If he provides it, or if the heirs acknowledge it, he is entitled to it from the deceased's estate.