הלכה אויף דברים 22:3

Since a person's domain can acquire property on his behalf without his knowledge, as will be explained, why does the owner of this courtyard not acquire the treasure buried within the old wall even if it originally belonged to the Amorites, and thus he would become its legal owner?

Our Sages derived this concept as follows: With regard to a lost object, the Torah Deuteronomy 22:3 states: "That is lost by him and found." This refers to an article that the owner lost, but others can find, thus excluding an article that fell into the sea and is "lost to him and all others." Surely, this applies to an ancient treasure that the person never owned. It is certainly "lost to him and all others." Therefore, it belongs to the finder.

Not to pretend not to have seen lost property, so as to save oneself the trouble of recovering it and restoring it to the owner, as it is said, “… thou mayest not hide thyself….” (Deut. 22:3).