Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 154
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 154, with English translation by Maimonides (Rambam).
לשבות בשבת, שנאמר: "וביום השביעי תשבות" (שמות כג,יב; שמות לד,כא).
To rest on the Sabbath, as [Exodus 23:12] states: "Rest on the seventh day...."