Halakhah zu Wajikra 23:22

That is that He commanded us to leave over the gleanings. And that is His saying, "you shall not gather the gleanings of your harvest" (Leviticus 23:22). And it too is a negative commandment that is rectified by a positive commandment, as is explained about the corner in Tractate Makkot. And the regulations of this commandment have already been explained in Tractate Peah. But by Torah law, it is only practiced in the Land [of Israel]. (See Parashat Kedoshim; Mishneh Torah, Gifts to the Poor 1.)

He prohibited - not to harvest all of what is planted. Rather one must leave some at the end of the field for the poor. And that is His saying, "you shall not completely cut the corner of your field" (Leviticus 23:22). And this negative commandment is rectified by a positive commandment: That is that, if he transgressed and cut all of what is planted, he may give the amount of the corner from what is harvested - and that is His saying, "you shall leave them for the poor and the stranger" - as we explained in the Positive Commandments (Sefer HaMitzvot, Positive Commandments 120). And [the commandment of] the corner is practiced with trees just like it it is practiced with fields; but this commandment is only practiced in the Land of Israel from [the law of] the Torah. And the regulations of this commandment have already been explained in the tractate that is connected to this (Peah). (See Parashat Emor; Mishneh Torah, Gifts to the Poor 1.)

He prohibited - not to glean the sheaves that fall in the field at the time of the harvest. Rather one must leave them for the poor. And that is His saying, "you shall not gather the gleaning of your harvest" (Leviticus 23:22). And this too is rectified by a positive commandment, like we explained about the corner. And the regulations of this commandment have already been explained in Tractate Peah. (See Parashat Emor; Mishneh Torah, Gifts to the Poor 1.)