Tanach - Deuteronomy
Deuteronomy 22:1-3:1
The Torah commands that if one sees another's lost item, they must not ignore it. They are obligated to return it to the owner, outlining the principle of hashavat aveidah (returning lost items).
לֹֽא־תִרְאֶה֩ אֶת־שׁ֨וֹר אָחִ֜יךָ א֤וֹ אֶת־שֵׂיוֹ֙ נִדָּחִ֔ים וְהִתְעַלַּמְתָּ֖ מֵהֶ֑ם הָשֵׁ֥ב תְּשִׁיבֵ֖ם לְאָחִֽיךָ׃ וְאִם־לֹ֨א קָר֥וֹב אָחִ֛יךָ אֵלֶ֖יךָ וְלֹ֣א יְדַעְתּ֑וֹ וַאֲסַפְתּוֹ֙ אֶל־תּ֣וֹךְ בֵּיתֶ֔ךָ וְהָיָ֣ה עִמְּךָ֗ עַ֣ד דְּרֹ֤שׁ אָחִ֙יךָ֙ אֹת֔וֹ וַהֲשֵׁבֹת֖וֹ לֽוֹ׃ וְכֵ֧ן תַּעֲשֶׂ֣ה לַחֲמֹר֗וֹ וְכֵ֣ן תַּעֲשֶׂה֮ לְשִׂמְלָתוֹ֒ וְכֵ֣ן תַּעֲשֶׂ֗ה לְכׇל־אֲבֵדַ֥ת אָחִ֛יךָ אֲשֶׁר־תֹּאבַ֥ד מִמֶּ֖נּוּ וּמְצָאתָ֑הּ לֹ֥א תוּכַ֖ל לְהִתְעַלֵּֽם׃ {ס}
If you see your fellow Israelite’s ox or sheep gone astray, do not ignore it; you must take it back to your peer. If your fellow Israelite does not live near you or you do not know who [the owner] is, you shall bring it home and it shall remain with you until your peer claims it; then you shall give it back. You shall do the same with their donkey; you shall do the same with their garment; and so too shall you do with anything that your fellow Israelite loses and you find: you must not remain indifferent.