Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 163
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 163, with English translation by Maimonides (Rambam).
לשבות בראשון של חודש השביעי, שנאמר: "באחד לחודש, יהיה לכם שבתון" (ויקרא כג,כד).
To rest on the first day of the seventh month, as [Leviticus 23:24] states: "On the first day of [this] month, you shall have a day of rest."