Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 213
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 213, with English translation by Maimonides (Rambam).
שלא ללקוט פרט הכרם, שנאמר "ופרט כרמך לא תלקט" (ויקרא יט,י).
Not to gather individual [fallen grapes], as [Leviticus, ibid.] states: "Do not gather the individual [fallen grapes] in your vineyard."