Sefer HaChinuch ספר החינוך

To leave what is forgotten to the poor: That we were commanded when we forget a sheaf in the field to leave it there, and that we not return to take it when the thing becomes known to us. And about this is it stated (Deuteronomy 24:19), “and you forget a sheaf in the field [...]; it shall go to the stranger, the orphan, and the widow” — meaning to say, leave it there for them.

It is from the roots of the commandment [that it is] since the poor and destitute — in their sin and in their poverty — suspend their eyes upon the produce, in their seeing the owners of the field sheaving their sheaves “according to the blessing of the Lord that He gave to them”; and they think in their heart, saying, “If only it will be like this for me, to gather sheaves into my house — and if only I could bring one, I would rejoice in it”; and hence it was from His kindnesses towards His creatures, may He be blessed, to fulfill this desire of theirs when it occurs that the owner of the field forgets it. There is also a benefit for the owner of the field, that he acquires through this a goodly soul; for truly through the trait of generosity and a blessed soul that does not place its heart upon the forgotten sheaf and leaves it to the destitute — on those with such a soul — does the blessing of God descend forever.

And from the laws of the commandment is that, which they, may their memory be blessed, said (Mishnah Peah 6:6 and see Mishneh Torah, Gifts to the Poor 5:18), “If a sheaf has [a volume of] two seah and he forgets it, it is not [considered] forgotten” — as it states, “and you forget a sheaf” — not a stack. And [also] that which they said (Mishnah Peah 5:7 and see Mishneh Torah, Gifts to the Poor 5:18), “A sheaf that is forgotten by workers and not forgotten by the property owner, or that is forgotten by the property owner and not forgotten by the workers,” or that it is forgotten by both of them, but there were others there that did not forget it — it is not [considered] forgotten until it is forgotten by every person. And the rest of its details are elucidated in Tractate Peah. (See Tur, Yoreh Deah 332.)

And this commandment is practiced by males and females in the places that priestly tithes and tithes are practiced. And I have already written at length [about] the whole matter of priestly tithes and tithes and the places where they are practiced in the Order of Shoftim, concerning the commandment of separating the great tithe (Sefer HaChinukh 507). And one who transgresses this and returns to go back to take it has violated this positive commandment and shows about himself [that he has] an evil soul.