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.)