Can I keep money paid to me by mistake?
Money that arrives by mistake is not yours, and the fact that someone else made the error does not transfer ownership. Islamic law treats property that comes into your hands without a valid basis as a trust you hold for its owner, and the Quranic instruction to render trusts to those they are due applies directly. So a bank crediting you twice, an employer overpaying your salary, a refund issued in error or a transfer sent to the wrong account all create an obligation to notify and return. Three things people ask about. Whether you must volunteer it or only return it if asked - most scholars say you must tell them, because staying silent while knowingly holding someone's property is concealment. What happens if the owner cannot be found after genuine effort - the established position is to give the amount away on their behalf. And whether a long delay changes anything - it does not; the obligation does not lapse with time, though how you settle it can be discussed if repaying at once would cause real hardship.