Question: A man inherited wealth from his father, and his father had been chaste, scrupulous regarding people’s wealth, and religiously committed. Then, after twenty-five years, a man came to that heir and said to him: “Such-and-such an item was not your father’s; rather, it belonged to so-and-so.” Then another man came and said the same. This is while that so-and-so has never claimed nor requested that item, neither before nor after, and we have remained in possession of that item during the lifetime of the deceased and after him. What is required of us in this regard?
Answer – and Allah is the One who grants success: If the matter is as described, then there is no problem and no sin, and nothing is required of you. So dispose of that item as you wish. However, if the man who is said to own the item were to make a claim before the judge and establish sound, just, conclusive proof that it is his property, then it would be obligatory upon you to comply with the judgment.
Yes, if the heir attains full knowledge that this item does indeed belong to so-and-so, then it is obligatory to hand it over to him without quarrelling or disputing.
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2