The 120th mitzvah is that we are commanded to leave over [for the poor] the corner (pe'ah) of [a field of] grain, [a tree of] fruit, etc.

The source of this commandment is G‑d's statement1 — after mentioning [several prohibitions, including taking for oneself] the corner of the field — "Leave them over [for the poor and the stranger]."

In tractate Makkos,2 it is explained that this mitzvah of pe'ah is a prohibition with a remedial positive commandment (lav shenitak l'aseh). The prohibition3 is contained in the verse,4 "Do not completely harvest the corners of your field." The positive commandment is contained in the verse, "Leave them over for the poor and the stranger."

The details of this mitzvah are explained in tractate Pe'ah.

The Biblical prohibition applies only in Eretz Yisroel.5