Is it permissible for the deceased debtor to take the amount paid to him by the debtor's sons for work that was not completed, and consider it as a settlement for their deceased father's debt, even though he had previously announced that he forgave their father and acquitted him?

A man is not entitled to claim a debt after he has absolved the deceased from it, because the debt is nullified by absolution, and what is nullified does not return. So, when a person relinquishes a right that he is permitted to relinquish, that right is nullified and does not return after its relinquishment.