121:5 On 9 Av, it was decreed that our ancestors in the wilderness would not be brought into the land of Israel. That was when the spies returned and the Jews cried for no good reason. It was therefore decreed that future generations would have reason to cry on this day. This was the day of great destruction, on which both the first and the second Temples were destroyed. The metropolis of Beitar was captured, killing tens of thousands of Jews. On this day, Turnus Rufus plowed the heichal (the entrance to the Temple) and the surrounding area, fulfilling the prophecy of Jeremiah 26:18, “Zion will be plowed like a field.” There is one more public fast, the Fast of Esther, which is discussed later, in 141:2.
121:6 If these fasts fall on Shabbos, they are pushed off until after Shabbos. However, if 10 Teves falls on Friday, one fasts the entire day.