Shemirat HaLashon שמירת הלשון

And, especially, if one has a time set aside for Torah in the house of study, how much will the trait of guarding his tongue avail his learning that it not be disturbed! For failing that he runs the risk of losing learning every day, and his learning itself will be fragmented. And the greatness of the punishment for this is well known. As Chazal have said (Avodah Zarah 3b): "If one interrupts his Torah study to engage in talk, he is fed broom-coals, as it is written (Iyyov 30:4): 'Those who interrupt maluach [(homiletically) "words written on the tablets" (luchoth)] with [idle] talk, broom-coal roots are their bread.'" And this is measure for measure. For if one studies Torah, his soul endures forever by the light of the holy Torah, which does not consume the soul (G-d forbid), but, to the contrary, sustains it eternally, as bread sustains his body in his lifetime. For this reason, Torah is called "bread," as it is written (Mishlei 9:5): "Come, eat of My bread, etc." And if he stops in the middle of his learning, he indicates that he does not want that bread, wherefore, he is fed there — instead of the food of the soul, the light of Torah — the light [i.e., the fire] of broom-coal roots.

Why broom trees, specifically? Because those coals made from a broom tree do not burn out for twelve months, as Chazal have said (Bava Bathra 74b), to teach us that he is judged for this like a rasha [a wicked one], whose punishment in Gehinnom lasts for twelve months. And this is the language of the holy Zohar in Parshath Shelach:

"If one interrupts words of Torah for idle talk, his life is 'interrupted' from this world and his judgment awaits him in the world to come."

[And, in truth, it would seem to me as good counsel for one who would like to guard his mouth and his tongue from forbidden speech, to teach himself not to speak at all in the house of study or the house of prayer. For aside from this being a great mitzvah in itself because of the sanctity of the place, as the holy books write, it is also of great avail to us in other respects 1) that the Torah one studies in the house of study and his prayers be complete, not lacking any answering of "Amen" and "Amen yeheh shmer rabbah" and "Barchu", 2) that through this there be in the accounting of the days of his life about ten years free of forbidden speech. For a Jew is found during the day in the house of study for his prayers and for some time after his prayer, for at least four hours a day, especially if he also has a set time for Torah study every day in the house of study for about two hours. Attending to this, about one-fourth of the full day is spent by him in Torah and prayer. If so, how good it will be for him when a fourth part of the days of his life will be added in which there will not have been any forbidden speech, but only Torah and prayer, 3) that though through this it becomes easier for him every day, too, to guard his faculty of speech, having taught himself every day to suppress it five or six hours all the time that he sat in the house of study.]