By Rabbi Berach Steinfeld
The Bais Yosef in Siman 550 brings in the name of the Avudraham that Asarah B’teves is different than all other fast days since if it would have fallen out on Shabbos it would not be pushed off to a different day. The posuk in Yechezkel 24:2 uses the terminology “Beetzem … Hayom Hazeh.” The Torah uses this terminology regarding Yom Kippur. The Avudraham adds that Asarah B’Teves can fall out on Friday, so we do fast on Friday. Unlike the other fast days which don’t fall out on a Friday.
The Rishonim argue on the above premise. Rashi in Megillah 5a says regarding the fact that if Tisha Be’Av falls out on Shabbos we push it off to Sunday, the same rule applies to Shiva Asar Be’Tamuz and Asara Be’Teves that if they fall out on Shabbos then we push it off until Sunday. There are many Rishonim that agree with Rashi, including the Meiri, the Rambam and the Kol Bo. They all say that if Asara B’Teves comes out on Shabbos we do not fast on Shabbos, unlike the above mentioned Avudraham.
We can explain this machlokes based on the Minchas Chinuch, mitzvah 301 that says the four Rabbinical fasts were not appointed to a particular day of the month, but rather one day of the designated month needs to be a fast day. The months we need to fast in are Teves, Tamuz, Av and Tishrei, but not on a particular day of the month. That is why the posuk in Zechariah 8:19 just calls them Tzom Horevii, Tzom Hachamishi, Tzom Hashvii and Tzom Hoasiri. Reb Chaim Brisker, in his stencils, asks based on the Avudraham why is Asara B’teves different than all other fast days? He answers that all other fasts are identified by the month and don’t have to be on a particular day, but Asara B’teves, where the posuk in Yechezkel says beetzem Hayom … shows us that the day of the month is also part of the identification of the taanis. This would be like a taanis chalom which one cannot push off!
The question is, why does the posuk call it Tzom Ho’asiri?  The Dikdukei Sofrim don’t have the girsa in the Gemara mai asiri asiri lechodoshim. The machlokes would be based upon whether we have the girsa in the Gemara of Asiri Lechodoshim, then it would be like Rashi and all other Rishonim that say that it is not docheh Shabbos. On the other hand, the Avudraham would not have that girsa, hence he held that Asara BeTeves was davka on Yud Teves and it would be docheh Shabbos. This could be the reason that when it does come out on Friday we fast into Shabbos and we don’t break the fast before Shabbos.
The Sefer Bais Moed drush 15 says that just like the beginning of all punishment began on Asara B’Teves and thereafter all the other fasts came about, so too, when we will have hatzlacha and have the Bais Hamikdosh rebuilt etc. it will begin on Asara BeTeves. That is why the posuk, when it enumerates the fast days beginning with Asara BTeves and ending with Tzom Gedalia, says that it will turn over into days of Sasson and Simcha. The posuk uses the terminology of yiheyeh and yihyu; it will begin with the first one mentioned and turn into a zeman of Simcha.
May we be zocheh to the Geulah Sheleima and have the Simcha of Asara BeTeves.
{Matzav.com}