How is the value of a father's debt, amounting to 90 Saudi Riyals (silver or French) from his youth, calculated, and how can it be repaid when the creditor is unknown?

If the currency becomes unavailable and the debt is due, it must be repaid with its value on the day it became unavailable. This value should then be given as charity on behalf of the creditors if there is no hope of reaching them or their heirs, and this act ensures the debt is settled. Sheikh al-Islam Ibn Taymiyyah clarified that whoever holds money belonging to others and despairs of knowing their owners should give it as charity on their behalf or spend it on the welfare of Muslims. One should hasten to pay off the debt of the deceased, for the soul of a human being remains suspended by their debt until it is paid off on their behalf.