Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 222
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 222, with English translation by Maimonides (Rambam).
שלא לקצור ספיחי שביעית כדרך שקוצרין בשאר השנים, שנאמר "את ספיח קצירך לא תקצור" (ויקרא כה,ה).
Not to reap crops that grow on their own in the seventh year in the same manner as in an ordinary year, as [Leviticus 25:5] states: "Do not reap the crops of your harvest that grow on their own."