Halakhah su Pe'ah 1:9

(12) And in all instances, he transgresses at that time of speaking lashon hara and rechiluth, the mitzvah of learning Torah, which is an absolute positive commandment, as explained by the Rambam in (Hilchoth Talmud Torah 1) and in his Sefer Hamitzvoth (Positive Commandments 11) and by all the enumerators of the mitzvoth. And there is no limit to the reward of this mitzvah, which is over and against all of the mitzvoth, as explained in the Mishnah (Peah 1:1) and in Yerushalmi (Ibid). For all of the mitzvoth are not comparable to one pronouncement of Torah. And, conversely, the punishment for its neglect is over and against all of the transgressions, as Chazal have explained (Petichah d'Eichah Rabbati 2): "The Holy One Blessed be He 'overlooked' the sins of idolatry, illicit relations, and the spilling of blood; but He did not overlook the sin of neglect of Torah."
At other times, one goes clean of din "on high" for transgression of this sin [of neglect of Torah study] by reason of being occupied with earning a livelihood or in pondering how to gain one. But when he speaks lashon hara or rechiluth, how does his livelihood "gain" from this? And he also transgresses in this time of speaking [lashon hara] many negative commandments. As explained in Semag (Negative Commandments 13), we have been exhorted by the Torah in many negative commandments not to separate ourselves from Torah in any manner. For there is always some way in which one can fulfill the positive commandment of [studying] Torah — If he is a steady learner, through his learning; and if he is not a learner, he can study the holy works that are translated into the vernacular [Yiddish] in our time, such as Chovoth Halevavoth, Menorath Hamaor, and the like; and he need not remain idle from learning Torah, and speak lashon hara and rechiluth [instead].
And I have also seen this [idea] stated in the name of the GRA [the Gaon of Vilna], who explained the difference between din [judgment] and cheshbon [reckoning]. "Din" — one's being judged for the transgression itself; cheshbon — one's being held to account — at the time of judgment for transgression — for the time he could then have spent in fulfilling a mitzvah. "Woe unto us on the day of din!" What can we answer if the Holy One Blessed be He reckons against us (for each moment of idle, derogatory, talk and light-headedness, or rechiluth and lashon hara) even the transgression of neglect of Torah for that time alone! For, in truth, with each word of Torah learning, one fulfills the positive commandment [of Torah study] itself! And if one learns a chapter of Mishnayoth or a page of Gemara, he fulfills many hundreds of mitzvoth, as the GRA of blessed memory wrote in Sh'noth Eliyahu (Peah 1:1) in the name of the Yerushalmi. If so, the cheshbon comes to many thousands of holy words of Torah, each one of which is a great mitzvah in itself, that we have actively nullified, and against them, many thousands of transgressions of neglect of the positive commandment of Torah study that we have committed at that very time!
And how much more grievous is the sin if at the very time that one separates himself form Torah, he speaks lashon hara and the like. For with every demeaning remark that he makes against his friend, he transgresses a [distinct] negative commandment in itself, as mentioned in Makkoth 20b and in the name of Rabbeinu Yonah above. So that if we come to reckon only the transgression of separation from Torah for every moment of lashon hara, several hundreds of [transgressions of] negative and positive commandments are added thereto. And how much more so, when we add to this [the transgression of] many other negative and positive commandments that we have expatiated upon until now. One must, therefore, keep himself from the recital of such vanities!

From the laws of the commandment is that which they, may their memory be blessed, said (Mishnah Peah 1:1 at the beginning) that these sacrifices do not have a measure - that even one would suffice, whether it be an animal or whether it be a bird, a dove or a chick. And that he needs to go up to Jerusalem regardless with a sacrifice in his hand, or with money to buy the sacrifice in Jerusalem. But he is not exempted with [an object that has] the value of money. And [that] if he did not sacrifice his sacrifice on the first day, he is able to make it up for seven full days (Chagigah 9a) - so long as he be there on the first days. And the rest of its details - are [all] elucidated in Tractate Chagigah (see Mishneh Torah, Laws of Festival Offering 1).

To leave over the corner of the field: To leave over a corner from the produce, as it is stated (Leviticus 19:10), "to the poor and to the stranger shall you leave them," after it mentioned, "you shall not finish the corner of your field" (Leviticus 19:9). And the understanding of stranger [here] is a righteous convert (see Sifra Kedoshim 3:4). And so [too], any "stranger" stated in [the context of] gifts to the poor - as behold, it is written about the second tithe (Deuteronomy 26:12), "to the stranger, to the orphan and to the widow." And that is certainly the righteous convert - when undifferentiated - as its witnesses (the orphan and the widow) are by its side. And the same is the case for all of the gifts to the poor. And nonetheless they, may their memory be blessed, said (Gittin 59b) that we do not prevent them from the poor of the idolaters, due to the ways of peace. And the content of the corner, is that a person leaves a little of his produce at the end of his field at the time that he reaps. And there is no measure to this remnant by Torah writ, but the Sages gave a measurement to the thing (Mishnah Peah 1:2), and it is one in sixty parts.

To not finish the corner in the field: Not to harvest all of what is planted, but rather to leave a remnant from it to the poor in the edge of the field, as it is stated (Leviticus 19:9), "you shall not finish the corner of your field in your harvesting." And this negative commandment is rectified by a positive commandment, as it is stated (Leviticus 19:10), "to the poor and to the stranger shall you leave them, etc." - meaning to say, that if he transgressed and harvested all of the field, that he give the measure of the corner to the poor from that which is harvested. And that is rabbinically one in sixty parts, as they obligated us so; but from the Torah, it has no measure, as we learned in Mishnah Peah 1:1, "These are the things that do not have a measure: the corner, etc."