Siman 549

It is a known matter that it is a positive commandment from the Torah to cry out and to supplicate for any trouble that should not come, and to fast during them; and it will be explained in the laws of fasts. And there are days that all of Israel fasts on them because of the troubles that occurred on them, in order to awaken the hearts and to open the paths of repentance. And this shall be a remembrance of our evil deeds, and the deeds of our fathers that were like our deeds now, until it caused them and us those troubles. And by the remembrance of these matters we shall return to do good, as it is written: "And they shall confess their iniquity and the iniquity of their fathers" (Leviticus 26:40) (the Rambam, chapter five of fasts).

And there are four days: the third of Tishrei, on which Gedaliah son of Ahikam was killed, and the remaining coal of Israel was extinguished. And this was the cause for the intensification of the troubles. And the tenth of Tevet, on which the wicked Nebuchadnezzar leaned against Jerusalem. As it is written in Kings (II 25:1) and in Jeremiah (52:4), that in the ninth year of the reign of Zedekiah, in the tenth month on the tenth of the month—Nebuchadnezzar and all his army came against Jerusalem. And Ezekiel, who was in Babylonia with the exile of Jeconiah—the Holy One, Blessed be He, revealed this to him in prophecy on that very day, as it is written in Ezekiel (24:1-2): "And the word of Hashem came to me in the ninth year, in the tenth month on the tenth of the month, saying: Son of man! Write for yourself the name of the day, the very essence of this day, the king of Babylonia has leaned against Jerusalem on this very day." Meaning: that He commanded him to write the name of the day, that is the month and also this specific day, and he wrote "on the tenth of the tenth month," and the prophet did not know why He commanded him to write so. And after he wrote, He revealed to him: Know for yourself that the king of Babylonia leaned against Jerusalem on this very day, and through this everyone saw the true prophecy, that in Babylonia it was revealed to the prophet that day and that hour. For "the very essence of the day" is called the strength of the day, like midday. And because there were then false prophets who misled Israel, like Hananiah son of Azzur and his colleagues, who prophesied that the Beit HaMikdash would not be destroyed and Israel would not be exiled from their land, and they strengthened the hands of transgressors; and Jeremiah, who rebuked them that they should return to Hashem, and if not the Beit HaMikdash would be destroyed and Israel would be exiled—they placed him in the courtyard of the guard, and put him in a pit of mud, as is explained in Jeremiah; therefore Hashem informed Ezekiel the prophet in Babylonia that Jeremiah is a true prophet, and he prophesied in Babylonia everything that occurred in the Land of Israel, and because on the tenth of Tevet was the beginning of the troubles. Therefore they established it as a fast for generations. And it is found in the name of the early authorities that if the tenth of Tevet were to fall on Shabbat—it would override Shabbat, because it is written regarding it "on this very day" just as on Yom Kippur (Beit Yosef in siman 550 in the name of Abudarham). And we do not hold accordingly, as will be explained.

And on the seventeenth of Tammuz, five things occurred: the tablets were broken, the tamid offering ceased during the First House, the city of Jerusalem was breached during the destruction of the Second House, the wicked Apostomus burned the Torah, and he placed an idol in the Sanctuary. Similarly, on the ninth of Av, five things also occurred: [1] It was decreed upon Israel in the wilderness that they should not enter the Land. [2-3] And the House was destroyed the first time and the second time. For at the end of Kings (II 25:8-9) it is written: "And in the fifth month, on the seventh of the month, in the nineteenth year of King Nebuchadnezzar... came Nebuzaradan... and he burned the House of Hashem...". And at the end of Jeremiah (52:12) it is written regarding this same event "on the tenth of the month." And they said in Taanit, it was taught in a Baraita: It is impossible to say "on the seventh," since it was already said "on the tenth." And it is impossible to say "on the tenth," since it was already said "on the seventh." How is this so? On the seventh they entered the Sanctuary, etc., and on the ninth towards dark they set it on fire, and it continued burning the entire tenth day (Taanit 29a). [4] And Beitar was captured on it, and there were thousands and tens of thousands of Israel within it. And there was a king there, and many imagined that he was the King Messiah. But sins caused it and they were all killed, and they were also not given over for burial, and it was a great tragedy like the destruction of the Beit HaMikdash. [5] And on this day, which is prepared for calamities, the wicked Turnus Rufus plowed the Sanctuary, to fulfill that which was said: "Zion shall be plowed as a field."

And these four fasts—they are explicitly stated in the Tradition through the prophet Zechariah (8:19): "Thus said Hashem of Hosts: The fast of the fourth, and the fast of the fifth, and the fast of the seventh, and the fast of the tenth, shall be to the house of Judah for joy and gladness." "The fast of the fourth" is the seventeenth of Tammuz, which is in the fourth month; and "the fast of the fifth" is the ninth of Av, which is in the fifth month; and "the fast of the seventh" is the fast of Gedaliah, which is the seventh of the months; and "the fast of the tenth" is the tenth of Tevet, which is the tenth of the months. And all Israel have the custom to fast on these days. And even though in the First Temple Jerusalem was breached on the ninth of Tammuz, as is written in Kings there, nevertheless they did not establish the fast on it but rather on the seventeenth, for in the Second [Temple] the city was breached on that day. And for us, the destruction of the Second Temple is more severe, for since then we have been impoverished and scattered to the four corners of the world. And to establish that they should fast on the ninth and on the seventeenth—one does not decree upon the community excessively. (And the Beit Yosef brought in the name of our teacher Yerucham that Gedaliah was killed on Rosh Hashanah, and it was postponed to the next day, see there. And nevertheless, it does not have the law of a postponed fast regarding a baal berit, since in all years it is so. And it is not similar to a fast postponed from Shabbat to Sunday, where everyone sees the postponement, which is not the case with the fast of Gedaliah, where all years are equal. And like the conclusion of the Taz, see there.)

In the Gemara ibid., it is derived from the verses in Zechariah that during the time of the Temple, these fasts were for joy and gladness, and so it shall be in the future, if God wills. And during the time of the destruction, when the children of Israel dwell in distress—they are obligated to fast. And it is a positive commandment of the words of tradition, and all of Israel accepted it upon themselves. And during a time when they do not dwell in distress: if the majority of the community desired—they fast; if they did not desire—they do not fast. And nowadays they have desired, and accepted upon themselves to fast (Tur). And especially now there is distress. Nevertheless, we did not accept them upon ourselves as a complete communal fast to begin the fast while it is still day, and to go barefoot, and regarding washing and anointing, and marital relations, except on Tisha B'Av alone, because then the troubles intensified against us, and it is not dependent on desire. But on the other three fasts, one eats at night, and we do not practice all the stringencies, but rather fast from morning until evening according to the law of an individual fast. And nowadays, in our many sins, people treat these fasts with disrespect, and they are destined to give an account. For anyone who is healthy—it is forbidden for him to separate from the community, and he violates a positive commandment of the words of tradition. And even one who must eat due to his weakness—he should not eat his meal as on all other days, but rather food and drink for the sustenance of his body alone. And so we practice.