Five tragedies occurred on Tisha B’Av. It was decreed that those who left Egypt would not enter the land of Israel, the first and second Temples were destroyed, the city of Betar was captured with thousands massacred, and Turnus Rufus plowed the site of the razed Temple. Consequently, Tisha B’Av was declared a day of national mourning and a fast day.
The fast of Tisha B’Av begins at sunset on the night preceding the fast day itself. In order to prepare oneself for the fast, the accepted custom on a weekday is to eat a regular meal without meat and wine before Minchah. Following Minchah, the last meal before the fast, the seudah mafseket, is consumed. This meal, eaten sitting on the floor, consists of bread, water, and an egg dipped in ashes (Shulchan Aruch, 552:6, Mishnah Berurah, 16). The seudah mafseket may not be eaten as a family meal but rather as an individual one, each person in his or her own corner with Birkat HaMazon recited by each person for himself without a mezuman (SA, ibid, 552:8).
When Tisha B’Av occurs on Shabbat, the fast is postponed. It begins on Motzaei Shabbat and ends Sunday night. When the fast is postponed to Sunday or when Tisha B’Av occurs on Sunday, the final meal eaten before the beginning of the fast is the seudah shelishit, the third meal of Shabbat. Since it is still Shabbat, during which mourning is prohibited, none of the restrictions of the seudah mafseket described above apply. Accordingly, one may eat meat, drink wine, sit around the table, and recite Birkat HaMazon with a mezuman, and there is no requirement to dip an egg in ashes. The only difference between this seudah shelishit and others eaten during the year is that this one must be terminated before the sun sets and the fast begins.
Because the words of Torah gladden the heart, studying Torah is forbidden when Tisha B’Av is on a weekday, except for passages in Scripture that deal with the destruction of the Temple and other calamities. When Erev Tisha B’Av or Tisha B’Av itself occurs on Shabbat, Torah may be studied, without restriction, on Shabbat morning and, according to many opinions, also on Shabbat afternoon. At Minchah on Shabbat Tisha B’Av or Shabbat Erev Tisha B’Av, the prayer Tzidkotchah is omitted as well as Pirkei Avot.
When Erev Tisha B’Av or Tisha B’Av itself occurs on Shabbat, the prayer V’he Noam is omitted because it was composed for recital at the inauguration of the Temple, whereas Tisha B’Av commemorates the destruction of the Temple. The prayer of Vayitein Lechah is also omitted. Kaddish Shalem is recited without Titkabel.
The procedure with Havdalah is as follows: For those who are fasting, first, the Havdalah blessing, Ata Chonantanu, is recited in the Amidah. Then, before reciting Megillat Eichah, the blessing Borei Me’orei Ha’esh is recited over candlelight but the other blessings usually recited at Havdalah are omitted. Neither wine nor besamim is used on this Motzaei Shabbat. On the evening following the fast, Sunday night, the Havdalah blessing that was omitted on Motzaei Shabbat is recited over wine, but neither flame nor besamim is used. Those who are not required to fast recite Havdalah on Motzaei Shabbat but use a Chamar Medinah beverage (such as tea, coffee or beer).
When Tisha B’Av occurs on a weekday, leather shoes are removed before sunset. When Erev Tisha B’Av or Tisha B’Av occurs on Shabbat, individuals, in order not to display signs of mourning on Shabbat, remove their leather shoes at Ma’ariv after reciting Barchu. The chazzan first recites Baruch Hamavdil bein Kodesh Lechol and then removes them before Barchu.