Fasting

(3) ... it is written, "The merciful man does good to his own soul (Proverbs 11:17)," this [refers to] Hillel the Elder, who, at the time that he was departing from his students, would walk with them. They said to him, "Rabbi, where are you walking to?" He said to them, "To fulfill a commandment!" They said to him, "And what commandment is this?" He said to them, "To bathe in the bathhouse." They said to him: "But is this really a commandment?" He said to them: "Yes. Just like regarding the statues (lit. icons) of kings, that are set up in the theaters and the circuses, the one who is appointed over them bathes them and scrubs them, and they give him sustenance, and furthermore, he attains status with the leaders of the kingdom; I, who was created in the [Divine] Image and Form, as it is written, "For in the Image of G-d He made Man (Genesis 9:6)," even more so!...

Rabbi Elazar HaKappar the Great says: What is the meaning when the verse states, with regard to a nazirite: “And he will atone for him for that he sinned by the soul [nefesh]” (Numbers 6:11). But with what soul did this nazirite sin? Rather, the nazirite sinned by the distress he caused himself when he abstained from wine, in accordance with the terms of his vow. And are these matters not inferred a fortiori? And if this nazirite, who distressed himself by abstaining only from wine, is nevertheless called a sinner and requires atonement, then with regard to one who distresses himself by abstaining from each and every matter of food and drink when he fasts, all the more so should he be considered a sinner. Conversely, Rabbi Elazar says: One who accepts a fast upon himself is called sacred, as it is stated with regard to the nazirite: “He shall be sacred, he shall let the locks of the hair of his head grow long” (Numbers 6:5). Here too, one can apply an a fortiori inference: And if this nazirite, who distressed himself by abstaining from only one matter, wine, is nevertheless called sacred, then with regard to one who distresses himself by abstaining from every matter, all the more so should he be considered sacred.

The verse [Exodus 24:18] comes only to accord deference to Moses, as the entire nation heard God address him. Rabbi Natan says: Moses was in fact called to enter the cloud; however, his entrance was not for the purpose of sequestering and purifying him, rather, the verse comes only to cleanse the food and drink that was in his intestines, to render him like the ministering angels who require neither food nor drink.

when Rav Sheshet would sit in observance of a fast, after he prayed he said as follows: Master of the Universe, it is revealed before You that when the Temple is standing, one sins and offers a sacrifice. And although only its fat and blood were offered from that sacrifice on the altar, his transgression is atoned for him. And now, I sat in observance of a fast and my fat and blood diminished. May it be Your will that my fat and blood that diminished be considered as if I offered a sacrifice before You on the altar, and may I find favor in Your eyes.

Mar Zutra said: The primary reward for fasting is for the charity given to the poor on the fast day (see Isaiah 58).

Rabbi Elazar says that Rabbi Yitzḥak says: Every fast day on which the distribution of charity [tzedaka] is left overnight, this is considered as if one spilled the blood of the poor people, as they fasted all day in the expectation that they would receive charity before the day was over in order to purchase food with which to break their fasts. ... The Gemara clarifies: And this statement applies with regard to the delaying of the distribution of bread and dates, which are ready to be consumed; but with regard to the delaying of the distribution of money, wheat, and barley, we have no problem with it.