Jewish Law

What’s the Truth about… Asarah B’Tevet Falling on Shabbat?


Misconception: If the tenth of Tevet (Asarah B’Tevet) would fall on Shabbat, it would be observed as a fast even on Shabbat.

Fact:  An important early authority, the fourteenth-century Spanish posek Rabbi David Abudraham, indeed says that Asarah B’Tevet would theoretically be observed on Shabbat. But most other authorities, from Rashi to the Shulchan Aruch, disagree, and the halachah is that it would be rescheduled like any other fast. Under our current fixed calendar, Asarah B’Tevet is unique among fast days in that it cannot fall on Shabbat, but it can fall on Friday; when it does (like this year—December 22, 2023), the fast is fully observed until its usual time and is broken at the Friday evening meal after dark.

Background: There are six standard fasts on the Jewish calendar, of which four relate to the destruction of the Beit Hamikdash and other national tragedies.1 These four are based on Zechariah 8:19, in which they are described as the fast of the fourth [month], the fast of the fifth, the fast of the seventh, and the fast of the tenth. 

The fast of the fourth is Shivah Asar B’Tammuz on account of, among other tragedies, Jerusalem’s walls being breached.2 The fast of the fifth is Tishah B’Av, in mourning of, among other major calamities, the burning of Jerusalem and the destruction of both the first and second Batei Mikdash.3 The fast of the seventh is Tzom Gedaliah on the third of Tishrei, observed due to the murder of Gedaliah ben Achikam (recounted in Melachim II 25:22–26 and Yirmiyahu 41), the final straw in the Babylonian exile. The fast of the tenth is Asarah B’Tevet,4 on account of the initiation of the siege of Jerusalem by the Babylonians under King Nevuchadnetzar II, which lasted over two years until they finally breached the walls and eventually conflagrated the city and Beit Hamikdash.5

The current fixed calendar has specific rules regarding which days of the week holidays and fasts can occur. With regard to the four fasts noted in Zechariah, three of them can fall on Shabbat. When Rosh Hashanah is on Thursday–Friday (a three-day yom tov even in Israel, which occurs 31.89 percent of years),6 Tzom Gedaliah is on Shabbat. Shivah Asar B’Tammuz and Tishah B’Av (which are always the same day of the week) can be on Shabbat (28.03 percent of years). When these fast days occur on Shabbat, the fast is pushed off and observed on Sunday (Mishnah Megillah 1:3 [5a]).7 Additionally, of these four, three can never fall on Friday. The fasts of Tammuz and Av can never fall on Monday, Wednesday or Friday, and Tzom Gedaliah can never fall on Sunday, Tuesday or Friday.8 Asarah B’Tevet is unique in two ways: it is the only fast that can fall on Friday and it is the only fast that cannot fall on Shabbat.

The dates on which fast days may and may not occur are due to the current fixed calendar. But what if we returned to a calendar based on the testimony of witnesses and Asarah B’Tevet did fall on Shabbat?

The Abudraham made a remarkable statement. In comparing the various fasts, he observed (Sefer Abudraham, Seder Tefillot Hata’aniot, 23:13, p. 357 in 5775 ed.) that when any of the other fasts fall on Shabbat, they are postponed, but Asarah B’Tevet (which he does note cannot currently fall on Shabbat) would not be deferred if it fell on Shabbat. He says this is indicated by the phrase in Yechezkel 24:2 describing the initiation of the Babylonian siege of Jerusalem as “b’etzem hayom hazeh—this selfsame day.” This indicates that the fast must be that very day, similar to the verses concerning Yom Kippur in which that phrase is also used (Vayikra 23:29).9 The Abudraham does not provide a source for this radical assertion, but about 200 years later, in 1564, Rabbi Yissachar ben Mordechai ibn Sussan in Tzefat published his Tikun Yissachar about the Jewish calendar and made the same claim (p. 28a) about theoretically observing Asarah B’Tevet on Shabbat. Rabbi ibn Sussan quoted Teshuvot HaGeonim as his source; unfortunately, no such Teshuvot HaGeonim is known today.10

This is a radical assertion, because in general it is forbidden to fast on Shabbat, even a partial fast (Shulchan Aruch, OC 288:1; Kitzur Shulchan Aruch 77:20).11 There is an opinion that it is Biblically forbidden to fast on Shabbat (Biur Halachah 288:assur). But there are exceptions. Under certain conditions, one can undertake a ta’anit chalom, a fast because of a bad dream, on Shabbat (Rambam, Ta’anit 1:12; Shulchan Aruch, OC 288:4–5), although as a consequence of fasting on Shabbat, a fast to repent for violating oneg Shabbat must then be observed.

Not everyone agrees with the assertion of the Abudraham. The Tur (OC 550) makes a blanket statement that if any of the four fasts fall on Shabbat, it is postponed until Sunday. Commenting on this, the Beit Yosef, a contemporary of Rabbi ibn Sussan, quotes the Abudraham and then says he does not know the source of the Abudraham’s claim. The Beit Yosef then quotes Rashi’s comment on the Talmudic statement that when Tishah B’Av falls on Shabbat it is postponed—Rashi extrapolates that the same is true for Shivah Asar B’Tammuz and Asarah B’Tevet (Megillah 5a, s.v. aval).12 The Beit Yosef also quotes the Rambam (Ta’anit 5:5), who says that if any of the four fasts fall on Shabbat, it is delayed. Thus, Rashi and Rambam both explicitly reject the assertion of the Abudraham. The Shulchan Aruch (OC 550:3) and Aruch Hashulchan (OC 549:2) rule like them, and that seems to be the halachah—if any of the four fasts fall on Shabbat, even Asarah B’Tevet, it is pushed off.

While the Abudraham’s position is rejected as normative halachah, it led to various interesting explanations over the years.13 The Chatam Sofer suggests that Asarah B’Tevet is the most severe of the fasts because it commemorates the commencement of the tragedies, and in all subsequent years on that day G-d decides whether to bring the Redemption. Rabbi Yehonatan Eybeschutz says that the original Asarah B’Tevet was on Shabbat. Rabbi Chaim Soloveitchik of Brisk (Chiddushei HaGrach, Rosh Hashanah 18b, p. 91 in 5768 ed.) says that Zechariah 8:19, which details the fasts, describes them by a specific month, not a specific date; thus, the day within the month to fast is flexible so the fast can be postponed.14 Regarding Tevet, there is an additional verse in Yechezkel that pins it to a specific date, which might not be changeable even if it is Shabbat.

As noted, Asarah B’Tevet is the only fast that can fall on Friday15 (20.1 percent of the time), as it does this year (Dec. 22, 2023/5784) and again next year (January 10, 2025/5785). It will not land on Friday again until December 22, 2034/5795.16

As a general statement, when Asarah B’Tevet is on Friday, the liturgy17 for Ashkenazim is the same as a regular fast: Kriat HaTorah in Shacharit and Minchah (Shemot 32:11–14 and Shemot 34:1–10), Selichot in the morning, Haftarah (Yeshayahu 55:6–56:8)18 at Minchah, and reciting Aneinu in the Amidah; but there is no Tachanun or Avinu Malkeinu at Minchah (Rema, OC 550:3 and 566:1; Magen Avraham 550:6; Mishnah Berurah 550:11 and 566:5).19  

What about the fasting itself? On a regular Friday, one may not eat a large meal so as to enter Shabbat with an appetite (Shulchan Aruch, OC 249:2). On the other hand, except for pious people who fast every Friday (Tur, OC 249; Shulchan Aruch, OC 249:3), it is inappropriate to fast on Friday (Mishnah Berurah 249:18) as one then enters Shabbat in a famished state. For example, when a minor, non-tragedy-related fast such as Ta’anit Esther or Ta’anit Bechorot falls on Shabbat, it is moved earlier, and once it is being moved it is moved back to Thursday to avoid fasting on Friday.20 

Because of these considerations, there is a lengthy discussion in the Gemara (Eruvin 40b–41a) about how to conduct fasts on a Friday, which concludes with the halachah that one may fast and complete the fast. Among the Rishonim, there are two ways to understand the question under discussion—may the fast be completed until nightfall (tzeit hakochavim) or must the fast be completed until nightfall (Beit Yosef, OC 249)? The halachah follows the latter interpretation that the fast must be completed. Although the Mishnah Berurah cites an opinion that the fast of Asarah B’Tevet should end before dark (249:21), the Rema (OC 249:4), Kitzur Shulchan Aruch (121:6), Aruch Hashulchan (OC 249:10), Yechaveh Da’at (1:80; he says it is about fifteen minutes after sunset), and others21 rule that for a public fast, such as Asarah B’Tevet, one must fast until dark (tzeit hakochavim).

Rabbi Aharon Lichtenstein, in a beautiful analysis,22 asks an obvious question about Asarah B’Tevet: “Of all the fasts that appear in Tanakh, that of the Tenth of Tevet is, in terms of our consciousness of the destruction, the weakest. When we think of the Ninth of Av, we envision the Temple in flames; . . . . But all that happened on the Tenth of Tevet was that the King of Babylonia laid siege to Jerusalem. For some time, life continued more or less in its normal fashion. . . .” He explains that: “. . . after the destruction, we must trace its sources and mark its stages; we must look backward to events that are not earth-shattering and perceive how the seeds of the destruction on the Ninth of Av were planted on the Tenth of Tevet. . . .” He concludes: “This is the point that is unique to the Tenth of Tevet. Specifically that which does not seem so terrible, that which ‘we can live with’—that is what requires rectification on the Tenth of Tevet. . . . I do not know whether, on the Tenth of Tevet, the tragedy of the Ninth of Av could have been avoided; not everything is in man’s hands. But at the very least, there may have been a chance to avert the tragic conclusion. If not on the national level then at least on the personal level, each individual by means of his repentance on the ‘fast of the tenth month’ can turn the ‘fast of the fourth month’ and the ‘fast of the fifth month’ into days of joy and celebration.”

Asarah B’Tevet was the beginning of the end; it was the first domino to fall in what would be a long, drawn-out domino effect. The momentousness of the day can only be discerned in hindsight, looking backward in time from where it eventually led. Using a modern analogy, in chaos theory, the butterfly effect shows how small perturbations can lead to significantly divergent results further along in time. A message of Asarah B’Tevet is that one should not be complacent because things are still tolerable; the course of the ship should be righted while there is still time.

In the present, Asarah B’Tevet cannot fall on Shabbat, and thus the discussion is theoretical. As for the future? The Rambam concludes the Laws of Fasts (Hilchot Ta’aniyot 5:19) by stating, based on Zechariah 8:19, that in the future all the fasts will be abolished, and more than that, they will be transformed into holidays and days of rejoicing and happiness. 

Thus, Asarah B’Tevet will never be fasted on Shabbat—may it and all the fasts become holidays speedily in our day.    


1. The other two fasts are Yom Kippur and Ta’anit Esther.
2. Mishnah Ta’anit 4:6 and Rosh Hashanah 18b. Note that for the first Beit Hamikdash, the breach of the walls of Jerusalem occurred on the ninth of Tammuz (Melachim II 25:3–4; Yirmiyahu 39:2; Yirmiyahu 52:6–7). See Ta’anit 28b for the shift of the fast from the ninth to the seventeenth. The Shulchan Aruch (OC 549:2) explains that the fast is on the seventeenth because the second destruction was more extreme. Be’er Heteiv (OC 549:3) says the pious actually fast on both the ninth and seventeenth, but the rabbis did not want to impose two fasts on the general public. He also quotes the Yerushalmi’s fantastic statement that even in the First Temple, the walls of Jerusalem were breached on the seventeenth, but because of the troubles, the wrong date was recorded!
3. One verse (Yirmiyahu 52:12–13) says Churban Bayit Rishon occurred on the tenth of Av, while another verse (Melachim II 25:8–9) says it was on the seventh of Av. The Gemara (Ta’anit 29a) explains that on the seventh of Av, the Babylonians entered and began defiling the Beit Hamikdash, and this continued until the ninth; toward evening on the ninth, they set fire to the Temple, and it burned through the night and into the tenth day.
4. In addition to the fast on Asarah B’Tevet, the Shulchan Aruch (OC 580:2) mentions that the eighth and ninth of Tevet were also customarily observed as fast days, the eighth because that is when the Torah was translated into Greek, and the ninth for an unknown reason. Others explain that the ninth of Tevet was observed as a fast day because Ezra HaSofer died (Taz, OC 580:1) or because Queen Esther was taken to Achashveirosh on that day (Rema, Mechir Yayin, 2:16). See Sid Leiman, “The Scroll of Fasts: The Ninth of Tebeth,” Jewish Quarterly Review, vol. 74, no. 2 (October 1983): 174–95. 
5. See Melachim II 25:1, Yirmiyahu 52:4, Yechezkel 24:1–2. Yechezkel’s wife died the evening of Asarah B’Tevet (24:15–19).
6. Thanks to Rabbi Phil Chernofsky, the former longtime editor of the OU Israel Center’s Torah Tidbits, for the statistics.
7. Yom Kippur and Ta’anit Esther can also fall on Shabbat. Yom Kippur, the only Biblical fast of the six, is observed on Shabbat. Ta’anit Esther, which does not commemorate tragedy and is followed by Purim, is advanced to Thursday when it falls on Shabbat.
8. Yom Kippur and Ta’anit Esther also cannot fall on Friday. Neither of them can fall on Sunday, Tuesday and Friday. The rule that Yom Kippur cannot fall on Sunday and Friday is actually one of the foundation stones of the fixed calendar. This is because Chazal were wary of having two back-to-back days, Yom Kippur and Shabbat, on which all melachah is absolutely forbidden.  
9. Tosefet Berachah (Vayikra 23:29) thinks that the “B’etzem hayom hazeh” in Yechezkel is more similar to its use regarding Noach (Bereishit 7:13) or Avraham (Bereishit 17:23), in that it narrative context, rather than a command as it is with Yom Kippur. Professor Daniel Sperber (Bekhol Derakhekha Daehu 30 [5775]:148-153) insightfully notes that in that verse in Yechezkel, the phrase actually appears twice, the first as a command and the second as narrative.
10. Because Rabbi ibn Sussan did not mention the Abudraham and cited an unknown Teshuvot HaGeonim, it is possible that he was actually referring to the Abudraham with that title. Or it is possible there was such a responsum, and that would answer the Beit Yosef’s puzzlement as to the source for the Abudraham.
11. It is because of this that the Magen Avraham (584:4) says that when Rosh Hashanah falls on Shabbat (as it did this year and will again four times in the next ten years), davening should not extend past halachic noon.
12. Interestingly, the Gemara does not discuss Asarah B’Tevet falling on Shabbat, something that was possible prior to the fixed calendar, an indication against the Abudraham. It does discuss, for example, Tishah B’Av on Friday (Eruvin 41a).
13. The three citations in this section are found in Bekhol Derakhekha Daehu 30 (5775): 148–53.
14. This idea is also found in the Minchat Chinuch (mitzvah 301), where, contrary to Rabbi Chaim Brisker, he applies it to Tevet.
15. Unlike all other fasts, there are only two days on which Asarah B’Tevet cannot fall: Monday and Shabbat. (The rarest day of the week for Asarah B’Tevet is Wednesday, which will not occur again until 2051/5812 and then 2078/5839, and occurs a mere 5.87 percent of the time.) 
16. It last occurred in 2020/5781, and before that in 2013/5774. As noted, it is actually not that rare, but people often perceive it as such, and thus every time it happens there is excitement. 
17. Except for Tishah B’Av and Yom Kippur, showering is permitted on the other fasts. Although there are those who recommend observing the other prohibitions, such as not showering, on the other fasts (Mishnah Berurah 580:6; Sha’ar Ha’tziyun 550:8–9), even they permit hot showers on a Friday Asarah B’Tevet because of kavod Shabbat (Mishnah Berurah 580:6).
18. Because of the Torah Reading and Haftarah (and in Israel, Birkat Kohanim), Minchah should be started earlier than on a regular Friday.
19. Asarah B’Tevet is also observed as the yahrtzeit for those killed in the Holocaust who have no known yahrtzeit. The special Kel Maleh Rachamim memorial prayer should be said in the morning after the Kriat HaTorah as usual.
20. In discussing this halachah about Ta’anit Esther, the Midrash Tanchuma (Bereishit:4; 5b in 5738 ed.) says that the fast may not be on Friday as that would infringe on preparation for kavod Shabbat and “kavod Shabbat is preferable to 1,000 fasts.”
21. See Yabia Omer 6:OC:31 for an elaboration of all of the sources.


Rabbi Dr. Ari Z. Zivotofsky is a professor of neuroscience at Bar-Ilan University in Israel. 

This article was featured in the Winter 2023 issue of Jewish Action.
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