The 163rd mitzvah is that we are commanded to refrain from doing melachah on the first day of the month of Tishrei [i.e. Rosh HaShanah].

The source of this commandment is G‑d's statement,1 "The first day of the seventh month shall be for you Shabbason" [a day of rest.]

We have already explained2 the statement of our Sages, "The term Shabbason indicates a positive commandment."