Note from the “Kol HaLashon” Hebrew printing of sefer “Shmiras HaLashon”: This Midrash is quoted in “Iggeres HaGR”A”.
 The entire pasuk from “Koheles” reads as follows:
“All of the toil of the person is for his mouth, and also the soul will not be satiated.” (Koheles: 6; 7)
The explanation of some of the meforshim, including RaSh”I, is that the person works in order that he will have some food to put into his mouth. RaSh”I adds that the person toils also to his benefit in The World to Come.
The GR”A understands this pasuk in the context of the punishment which one may suffer through the toil involving that which he speaks with his mouth, and would consequently be punished for such forbidden speech.
 The passage from maseches “Chullin” (89a), states as follows:
“Rabbi Yitzchak said, ‘What is the meaning of that which is written, “If I were a mute, they would speak righteousness, they would judge people justly.” (Tehillim: 58; 2) What is the trade of a person in this world? He should act as a mute. Perhaps [this applies] even [in reference] to [involvement in speaking] words of Torah? The pasuk comes to teach us: “…you shall speak words of righteousness…” Perhaps [the person] can become haughty [through his study of Torah]? The pasuk comes to teach us: “…they will judge people justly.””
 “Sh’ole” refers to “gehinnom”, both of which are translated as “hell”.
 The entire pasuk reads, “Also in your thoughts do not curse the king and in your sleeping chambers, do not curse the wealthy [person], for a bird of the Heavens will carry the voice and The Master of Wings will relate the matter.” (Koheles: 10; 20)
RaSh”I explains that “the king” can either refer to HaShem who is The King of the Universe, or can refer to a human king. The “bird of the Heavens” refers to the person’s soul will carry the person’s thoughts and the angel which escorts the person during his lifetime will relate the matter which might seem to be hidden. RaSh”I explains that this “Master of Wings” can also refer to passersby, that being that anyone can hear that which was related in a seemingly secretive manner and relate that “hidden matter” to others.
 This section of the gemara from maseches “Avodah Zara” (18b), states as follows:
“Rabbi Shimon ben Lakish said: ‘All of those who [involve themselves in] mockery fall into gehinnom, as it says [in “Mishlei”], “The haughty sinner, his name is “laitz” - “mocker”, he acts with “evrah” - outpouring sin.” (21; 24) And evrah only refers to gehinnom, as it says [in “Tzifaniah”], “That day is a day of “evrah”…” (Tzifaniah: 1; 15)