Halakhah su Levitico 19:9

One does not look directly at the face of someone eating at the table, nor at the plate, nor at the portion set before him, so as not to embarrass anyone. The table server does not eat in the presence of the diners, but they give him some of each dish out of kindness, so that his heart won’t be ashamed. A host who has eaten before his guest – he’s a disgrace! When two are sitting at the table, the older gets to reach for the food first, then the younger. And whoever extends their hand before someone older than them – he’s a glutton! One leaves a “corner” of food uneaten in a kettle but not in a pot.¹⁵Derekh Eretz Rabba, 6. Corner in the Hebrew is “pe’ah.” Just as farmers are commanded to leave the corners (pe’ot) of their fields un-harvested for the poor to glean (in Lev. 19:9), so one should not scrape clean food served a cooking pot, but rather should leave leftovers for the servers to eat. On the other hand, it is okay not to leave leftovers from food served in a different kind of cooking pot. Chavel suggests that the difference between the “kettle” (lit., “something made in an ‘ilpas – one type of cooking pot”) and the “pot” (lit., something made in a kedrah – another type of cooking pot) is their size, and that one is only required to leave a “corner” of leftovers for the server from the bigger stew pot (ilpas), not the smaller cooking pot (kedrah). In other words, unlike the saying “That’s like the pot calling the kettle black,” what I’ve translated here as “kettle” and “pot” are significantly different types of cooking utensils. It happened to Rabbi Yehoshua when he was a guest at a widow’s home, that she brought him a stew pot, and he did not leave a “corner.” She brought him a second one, and he did not leave a “corner. The third time she ruined the dish with salt. He withdrew his hand and ate only bread. She said to him, “Why did you take so much bread when you took so little of the pounded beans?” Hence, Rabbi Yehoshua said, “Nobody has ever gotten the best of me except a woman who was a widow, a little boy, and a little girl.” For it happened to Rabbi Yehoshua when he was walking on a path through a field, that he found a girl who was sitting in the field. She said to him, “Why are you walking in the field?” He said, “I’m walking on a path.” She said, “If this is a path, it’s only because robbers like you have trampled it into one.” And again, it happened to Rabbi Yehoshua when he was walking on a path through a field, that he found a little boy sitting where the path split in two. He said to the boy, “My son, which path will take me into the city?” He said to him, “There are two paths in front of you: the one long and short; the other short and long.” Rabbi Yehoshua took the short and long path. When he got to the wall of the city, he saw gardens and orchards surrounding the city. R. Yehoshua turned back and saw the little boy sitting where he had been before. He said to him, “My son, didn’t I ask you which path would take me into the city?” He replied, “You’re the old sage; aren’t you wise enough to figure it out?” At that, Rabbi Yehoshua went to kiss him on his head and said, “Happy are you, O Israel, for all of you are wise, from your oldest to your youngest!¹⁶All these stories about Rabbi Yehoshua are taken almost verbatim from Derekh Eretz Rabba 6.”

That is that He commanded us to leave over the corner of the produce, the trees and that which is similar to them. And that is His, may He be exalted, saying, "you shall leave them" (Leviticus 19:10), after His mentioning, the corner. And it is explained in Tractate Makkot (Makkot 15b) that the [law of the] corner is a negative commandment that is rectified by a positive commandment. Indeed, the negative commandment is His saying, "you shall not wholly reap" (Leviticus 19:9); and the positive commandment is His saying, "you shall leave them." 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 us from taking the forgotten sheaves. And that is His saying, "and you forget a sheaf in the field, you may not return to take it" (Deuteronomy 24:19). And [the commandment of leaving what is forgotten] is practiced both with produce and with [fruit] trees; and is rectified by a positive commandment. For if one transgressed and took it, he is obligated to return it to the poor. And that is His saying, "it shall be for the stranger, the orphan and the widow." And the regulations of this commandment have already been explained in Tractate Peah. And know that the principle with us is that any negative commandment that has a positive commandment [attached to it] - if he fulfills the positive commandment in it, he is not lashed; but if he does not fulfill it, he is lashed. An example of this is that if he harvested the corner, he is not liable for lashes immediately when he harvested. Rather he must return the sheaves. And likewise if he threshed them, ground the wheat and kneaded the dough, he must give what was fit for him for [his obligation of] the corner, from the dough. But if it happened that the wheat got totally lost or it was burnt, he is lashed - as he did not fulfill the positive commandment in it. And all the more so if he negated [the positive commandment] actively - as when he ate all of the wheat. But do not think that that which they said, in the Gemara, Makkot (Makkot 16a) - "For us, we only have this and one other one," and it is explained that this other one is the corner - requires that this law is in fact only exclusively regarding the corner. Rather the matter of the "other one," is meaning to say, the corner and everything, the law of which is like the law of the corner - the single grapes, what was forgotten, the gleanings and the ollalot. Each one of them is a negative commandment that is rectified by a positive commandment and has the possibility within it - that is possible with the corner - of 'he fulfilled it or he did not fulfill it,' and 'he nullified it or did not nullify it.' For the verse from which we learned that there is a positive commandment with the corner is His, may He be exalted, saying, "you shall leave them for the poor and the stranger" (Leviticus 19:9-10); and that appears about the corner, the gleanings, [the single grapes,] and the ollalot. He said [there], "you shall not completely cut the corner of your field, [you shall not gather] the gleaning of your harvest. You shall not pick your vineyard bare; neither shall you gather the single grapes of your vineyard." And He likewise said about the forgotten sheave, "you may not return to take it." And once we have found the language in the Gemara, that the corner is a negative commandment rectified by a positive commandment and they brought a proof about the positive commandment in it from His saying, "you shall leave them for the poor and the stranger, etc." - it is a proof that these five commandments are [all] negative commandments that are rectified by a positive commandment. So - as we mentioned - as long as he fulfills the positive commandment in it, he is not lashed; but if the fulfillment of the positive commandment is no longer possible, he is lashed. However so long as it is possible to fulfill it - even though he has not fulfilled it - he is not yet lashed. Rather we only command him to fulfill it, until we know that he has already transgressed the negative commandment and there is no possible way for him to fulfill the positive commandment in it. Then he is lashed. And heed this content and understand it. (See Parashat Ki Tetzei; Mishneh Torah, Gifts to the Poor 1.)