וְכֵ֧ן תַּעֲשֶׂ֣ה לַחֲמֹר֗וֹ וְכֵ֣ן תַּעֲשֶׂה֮ לְשִׂמְלָתוֹ֒ וְכֵ֣ן תַּעֲשֶׂ֜ה לְכָל־אֲבֵדַ֥ת אָחִ֛יךָ אֲשֶׁר־תֹּאבַ֥ד מִמֶּ֖נּוּ וּמְצָאתָ֑הּ לֹ֥א תוּכַ֖ל לְהִתְעַלֵּֽם׃ (ס)
對他的驢，你也要這樣做；對他的衣服，你也要這樣做；你弟兄所失落的一切東西，你若找到了，也都要這樣做，不可轉眼不顧。
Mishneh Torah, Robbery and Lost Property
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?
Mishneh Torah, Robbery and Lost Property
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.
Mishneh Torah, Negative Mitzvot
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).