The 242nd mitzvah is that we are commanded regarding the law of an unpaid watchman.1

The source of this commandment is G‑d's statement2 (exalted be He), "If one person gives another money or articles to watch...."

The details of this mitzvah are explained in the 9th chapter of tractate Bava Kama, the 3rd chapter of Bava Metzia and the 8th chapter of Shavuos.