Giving in charity an amount her father gave her before his death to give to someone who could not be found

Q: I am now an old woman and I do not have any children. When I was middle-aged and my father was dying, he gave me a French Riyal. He told me that it belonged to someone from Shaqra’, but he did not tell me his name, or perhaps he did and I forgot it. I invested this French Riyal until it became four French Riyals. As I do not know who this man is, I gave the money away as Sadaqah (voluntary charity), and instead of the four French Riyals I gave five of our present day Riyals, as I had previously spent the four French Riyals I had. Please advise me how I can absolve myself of any possible liability.

A: You have to give as Sadaqah the value of the four French Riyals in banknotes on behalf of the owner of the money, after deducting the five Riyals that you gave before. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.