Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 199
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 199, with English translation by Maimonides (Rambam).
להשיב המשכון לבעליו, שנאמר: "השב תשיב לו את העבוט" (דברים כד,יג).
To return security to its owner, as [Deuteronomy 24:13] states: "You shall surely return the security to him."