We are commanded to cry out and to blow trumpets when the community is in distress, as it says "...For the adversary that distresses you blow the trumpets"¹; the sages instituted fasting and a special order of prayers on such occasions. Similarly, if an individual is in distress he should fast and pray for mercy.^a

All Israel are accustomed to fast on the third day of Tishrei, the tenth day of Teves, the seventeenth day of Tammuz, the ninth day of Av, and the thirteenth day of Adar in commemoration of events that happened on those days. If any of these fasts falls on the sabbath it is deferred to Sunday (except for that of the thirteenth of Adar which is held on the preceding Thursday). On all of them except the ninth of Av it is permissible to eat at night. In the days of the Messiah all of these fasts will become festivals, as it says "The fast of the fourth month [Tammuz] and the fast of the fifth month [Av] and the fast of the seventh month [Tishrei] and the fast of the tenth month [Teves] will become for the house of Judah good times of joy and happiness". ^2,b

From the beginning of the week in which the ninth of Av occurs one must not cut one's hair or wash clothes, and it is customary not to bathe or to eat meat. On the ninth of Av washing, anointing, wearing shoes, and sexual relations are forbidden just as on Yom Kippur. The sages instituted [these restrictions and various other signs of mourning] in commemoration of the destruction of the Temple.^c