Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 220
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 220, with English translation by Maimonides (Rambam).
שלא לעבוד אדמה בשביעית, שנאמר "שדך לא תזרע" (ויקרא כה,ד).
Not to cultivate the land in the seventh year, as [Leviticus 25:4] states: "Do not sow your field."