Positive commandment · Mitzvat Aseh #199 of 613
To return security to its owner
להשיב המשכון לבעליו
The verse · Devarim 24:13
הָשֵׁב תָּשִׁיב לוֹ אֶת־הַעֲבוֹט כְּבוֹא הַשֶּׁמֶשׁ וְשָׁכַב בְּשַׂלְמָתוֹ וּבֵרְכֶךָּ וּלְךָ תִּהְיֶה צְדָקָה לִפְנֵי ה׳ אֱלֹהֶיךָ
“thou shalt surely deliver him the pledge again when the sun goes down, that he may sleep in his own garment, and bless thee: and it shall be as righteousness to thee before the Lord thy God.”
The Rambam’s words
To return security to its owner, as [Deuteronomy 24:13] states: "You shall surely return the security to him."
להשיב המשכון לבעליו, שנאמר: "השב תשיב לו את העבוט" (דברים כד,יג).
Why · Sefer HaChinuch #587
To return the surety to the owners at the time that he needs it
“It is from the roots of this commandment that G-d, may He be blessed, desired, in His goodness, the good of His creatures and their merit and wanted that they should teach themselves the traits of kindness and mercy in order that they merit the good.”
Who & when
“And this commandment is practiced by males and females in every place and at all times.”
Where in the Mishneh Torah
Hilchot Creditor and Debtor הלכות מלווה ולווה