The 199th mitzvah is that we are commanded to return a security deposit to its Jewish owner when he needs it. If the objects are needed during the day, such as tools he works with, you must give them to him during the day and hold them only at night. If they are needed at night, such as a mat and blanket for sleeping, you must give them to him during the night and hold them only during the day.

In the words of the Mechilta: "The verse,1 'You must return it to him before sunrise' refers to a garment worn during the day, which you give to him for the entire day. What is the source for the law that a garment worn at night must be given to him for the entire night? The verse,2 'Return the security to him before the sun sets.' " Therefore our Sages said, "A day garment may be held at night and a night garment held during the day; the day garment is returned for the day and the night garment for the night."

It has already been explained in tractate Makkos3 that the verse4 "[When you make any kind of loan to your neighbor,] do not go into his house to take something as security" is a lav she'nitak l'aseh (a prohibition with a remedial positive commandment) — the positive command being "Return the security to him." In the words of the Sifri: "The verse 'Return [the security to him]' teaches that an article that is used during the day must be returned for the day, and one used at night for the night. A quilt is returned for the night and a plow for the day."

The details of this mitzvah are explained in the 9th chapter of tractate Bava Metzia.5