Negative commandment · Lo Ta’aseh #222 of 613
That we not harvest the aftergrowth on the seventh year
שלא לקצור ספיחי שביעית כדרך שקוצרין בשאר השנים
The verse · Vayikra 25:5
אֵת סְפִיחַ קְצִירְךָ לֹא תִקְצוֹר וְאֶת־עִנְּבֵי נְזִירֶךָ לֹא תִבְצֹר שְׁנַת שַׁבָּתוֹן יִהְיֶה לָאָרֶץ
“That which grows of its own accord of thy harvest thou shalt not reap, nor gather the grapes of thy undressed vine: for it shall be a year of rest for the land.”
The Rambam’s words
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."
שלא לקצור ספיחי שביעית כדרך שקוצרין בשאר השנים, שנאמר "את ספיח קצירך לא תקצור" (ויקרא כה,ה).
Why · Sefer HaChinuch #328
That we not harvest the aftergrowth on the seventh year
“It is from the roots of this commandment to affix in our hearts and make a strong impression in our minds [about] the matter of the world having been created.”
Who & when
“And this commandment is practiced from Torah writ by males and females in the Land of Israel at the time that Israel is there.”
Where in the Mishneh Torah
Hilchot Sabbatical Year and the Jubilee הלכות שמיטה ויובל