Answered by Ustadh Tabraze Azam
Question: I had a calculator in my bag. After studying l packed my bag and took someone’s calculator that looks exactly like mine. After days (maybe even weeks after) I realized it was not mine however I do not have the faintest clue who the calculator might belong to. What do I do with it? Please advise?
Answer: Wa alaikum assalam wa rahmatullah,
I pray that you are in the best of health and faith, insha’Allah.
If possible, take it back to the place where you accidentally picked it up, and hand it in to the staff there. This would be sufficient.
Otherwise, put up a public notice so that the owner can contact you.
However, if a significant amount of time passes such that you don’t expect to hear from the owner, you can: (a) give the monetary equivalent of the item in charity (on behalf of the owner), (b) keep the item until the owner shows up, or (c) sell the item (and keep the money for the owner).
[Ibn `Abidin, Radd al-Muhtar]
And Allah alone gives success.