Musar על עבודה זרה 6:14

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.