[The following is taken] from the holy letter of the GR”A, “Alim Li’Tirufah”:
“Everyone will be brought in judgment for every utterance, [that judgment will not overlook] even a “light utterance”. Therefore, I warn you to accustom yourself as much as possible to dwell in solitude, for the sin of the tongue is upon everything. [This follows] that which [our Sages] of Blessed Memory have said: “These are the things for which a person eats [their fruits in this world, and the principle remains for him to receive in The World to Come]… and Lashon HaRa is equivalent to all of them.” What [need is there] for me to go on at length concerning this sin [of Lashon HaRa] which is more severe than all of the [other] sins? [Concerning the phrase] “All of the toil of a person is for his mouth.”, (Koheles: 6; 7) – Our Sages of Blessed Memory have said [in Koheles Rabbah], that all of the mitzvos [one performs] and [the] Torah [that one learns], is insufficient [to combat] that which one utters from his mouth. What is the trade of a person in this world? He should [act] like a mute and he should stick his lips together like millstones… The entire arch of the slingshot, [with which he is punished], is due to the breath of his mouth that [he emits when he speaks] idle words. For each word of nonsense, his [soul] needs to be shot from one end of the universe to the other end [of the universe]. [This punishment] is entirely due to words of excess. However, [when one utters] forbidden words, such as Lashon HaRa, mockery, oaths, vows, [words of] dispute, and curses, specifically in the synagogue, and on Shabbos and Yom Tov, for these, one must descend very far downward [in] gehinnom. [The punishment is so great] that it is impossible to imagine the great afflictions and troubles that one suffers as a result of one utterance. No utterance [that one utters] is lost and left unwritten, for angels constantly go by every single person and [never] separate from him, [all the while] writing down every single utterance. [This follows that which is written in the following pasuk]: “For a bird of the Heavens will carry the voice and a master of wings will relate the matter.” (Koheles: 10; 20) [Another pasuk states]: “Do not allow your mouth to bring sin to your flesh, and do not say before the angel, ‘For it was negligence’, Why should [G-d become angry concerning your voice and destroy the work of your hands?]” (Koheles: 5; 5)…”
 The teaching from Devarim Rabbah reads as follows: ““…Do not allow your mouth to bring sin onto your flesh.” (Koheles: 5; 5) The rabbis say that this pasuk refers to habitual speakers of Lashon HaRa. To what does “…Do not allow your mouth [to bring sin against your flesh] refer? Is this really true [that the mouth brings sin upon the flesh]? Once the mouth [utters] the Lashon HaRa, it sins against the body, as it causes it to be stricken. [Therefore], “to bring sin to the flesh” [is literally the case], as the mouth sins against the flesh. What is the meaning [of the continuation of this verse from Koheles]: “…do not say before the angel that it was negligence.”? [This teaches that one should not say: “Behold, I will go and speak Lashon HaRa and no being will know [of my sin].” [For, in response to the aforementioned statement], The Holy One, Blessed is He, says to him: “You should be aware that I am sending an angel, and he will be standing at your side and will write [down] everything that you utter against your fellow.” What [is the source for an angel recording all of one’s words]? As it says, (Koheles: 10; 20) “Also in your thoughts do not curse the King…” Why? “…For a bird of the Heavens will carry the voice…” What is the meaning of “…and a master of wings will tell the thing”? These [“masters of wings”] are the angels, about whom it is written, “…six wings, six wings, for [each] one…” (Yeshayahu: 6; 10), “…Why shall G-d become angry about your voice? …” (Koheles: 5; 5) – Concerning that voice which you uttered from your mouth. “…And destroy the work of your hands.” – For that person is stricken with afflictions. If you do not believe this, behold, Miriam was afflicted as a result of speaking Lashon HaRa against her brother, Moshe. [We are commanded] “To remember that which [HaShem, your G-d did when you were on the path, when you left Egypt].” (Devarim: 24; 9) Due to this [sin of Lashon HaRa, Miriam] was stricken [with tzara’as].
 The GR”A (Acronym for Gaon Rav Eliyahu, Rabbi Eliyahu Kramer (1720 – 1797), commonly known as the Vilna Gaon (Great one of Vilna).
 Note from the “Kol HaLashon” printing of sefer “Shmiras HaLashon”: [The GR”A is referring] to that which we copied in the name of the [Talmud] Yerushalmi, [maseches] “Peah” (chapter 1, halacha 1). The GR”A also [wrote] this [teaching] down in his book “Shnos Eliyahu”, in the mishnayos of [maseches] Peah (chapter 1, mishna 1), in the commentary of the “Aruch”, beginning with the words “v’heivaisah shalom” – “and bringing peace”.