Is one absolved of responsibility by donating one hundred Riyals, seeking forgiveness, and praying for the deceased, in exchange for a fund taken without his knowledge that cannot be returned to his heirs?

If the rightful owner or their heirs are known and accessible, then the right must be delivered to them. It is not a condition to inform the heirs of the exact nature of the matter; rather, it suffices to deliver their right by any means. The amount returned to the heirs must not be less than the value of the usurped item on the day it was usurped.