The 240th prohibition is that we are forbidden from holding someone's security deposit during the time that he needs it. An article which is used during the day must be returned for the day, and one used at night for the night, as the Mishneh says,1 "A pillow is returned for the night and a plow for the day."
The source of this prohibition is G‑d's statement2 (exalted be He), "you may not go to sleep with his security." The Sifri explains, "[The verse means] 'you may not go to sleep with his security' in your possession." Instead, anything which he cannot replace due to his poverty must be returned to him, as explained in the verse,3 "[If you take your neighbor's garment as security, you must return it to him before sunset.] This alone is his covering, the garment for his skin."
The details of this mitzvah are explained in the 9th chapter of tractate Bava Metzia.
