Halakhah su Ta'anit 4:6
חֲמִשָּׁה דְבָרִים אֵרְעוּ אֶת אֲבוֹתֵינוּ בְּשִׁבְעָה עָשָׂר בְּתַמּוּז וַחֲמִשָּׁה בְּתִשְׁעָה בְאָב. בְּשִׁבְעָה עָשָׂר בְּתַמּוּז נִשְׁתַּבְּרוּ הַלּוּחוֹת, וּבָטַל הַתָּמִיד, וְהֻבְקְעָה הָעִיר, וְשָׂרַף אַפּוֹסְטֹמוֹס אֶת הַתּוֹרָה, וְהֶעֱמִיד צֶלֶם בַּהֵיכָל. בְּתִשְׁעָה בְאָב נִגְזַר עַל אֲבוֹתֵינוּ שֶׁלֹּא יִכָּנְסוּ לָאָרֶץ, וְחָרַב הַבַּיִת בָּרִאשׁוֹנָה וּבַשְּׁנִיָּה, וְנִלְכְּדָה בֵיתָר, וְנֶחְרְשָׁה הָעִיר. מִשֶּׁנִּכְנַס אָב, מְמַעֲטִין בְּשִׂמְחָה:
Cinque eventi accaddero agli antenati il diciassettesimo di Tamuz e cinque al nono di Av. Il diciassettesimo di Tamuz, le Tavole furono spezzate, l'offerta Tamid fu terminata, le mura della città furono violate, Apaustamous bruciò la Torah, un idolo fu posto nel cortile del tempio. Il nono di Av fu decretato ai nostri antenati che non gli sarebbe stato permesso di entrare nella Terra di Israele, il primo e il secondo tempio furono distrutti, Beitar fu catturato, la città di Gerusalemme fu arata. Da quando inizia il mese di Av, riduciamo la gioia.
Shulchan Arukh, Orach Chayim
Hagah: And so it is with a priest who goes up to recite the priestly benediction,100The priestly benediction, Birkhat Khohanim, ברכת כהנים, was also known as the Nesi'at Kapayim, נשיאת כפים, or the lifting of the hands. It was part of the daily service in the Temple every morning and evening before the thanks-offering the priests would raise their hands up and pronounce the three-fold priestly blessing from a special platform called a dukhan, דוכן. Therefore the ceremony has also been referred to as the dukhenen. The ceremony was transferred into the daily service in the synagogue. In Ashkenazi communities it is restricted to the Musaf, Additional Service (see footnote 166) of festivals but is omitted on Simḥat Torah because the Kohanim might be drunk and when the festival falls on the Sabbath. It is said during the Amidah (see footnote 43) of the Musaf Service during the fifth (of seven) benediction which calls for the restoration of the Temple Sacrifice Service where the priests served in performing the sacrifices for the people to God.
The Hebrew text of the blessing Numbers 6:24, consists of three short verses of three, five, and seven words respectively. It mounts in gradual stages from the petition for material blessing and protection, to that of a divine favor as a spiritual blessing, and it climaxes in a petition for God's most consummate gift of peace, which encompasses the welfare of all material and spiritual wellbeing. These fifteen words have a rhythmic beauty to them. They are introduced by a reminder of the Temple Sacrifice Service and a prayer for its reestablishment. The blessing was only spoken by Aaron but it was a blessing of God.
The words that the descendents of the priests chanted in front of the congregation from the ark covered by their prayer shawls with their fingers separated in the middle are as follows:

The Lord bless thee and keep thee:
The Lord make his face to shine upon thee, and be gracious unto thee:
The Lord turn his face unto thee, and give thee peace.
And the congregation responds "Amen" to each blessing.
Hertz, op. cit., pp. 834-37. he washes his hands even though they are clean because the majority of (the instances of) washing which are not intended for pleasure are permitted, (הגהות מיימוני פ״ב מהל׳ י״כ ומהרי״ל).101Hagahot Maimuniyyot, chapter two from the Laws of Yom Kippur and Maharil, הגהות מיימוני פ״ב מהל׳ י״כ ומהרי״ל.
For Hagahot Maimuniyyot, הגהות מיימוני; see footnote 27.
For Maharil, מהרי״ל; see footnote 8. Therefore even if one comes from the street and his feet are dirty, it is permissible to wash them, (ב״י בשם הגהות מיימוני וסמ״ג וטור הלכות ט״ב).102Beit Yosef in the name of Hagahot Maimuniyyot and Sefer Mitzvot Gadol and Tur on the Laws of Tishah be-Av, ב"י בשם הגהות מיימוני דסס"ג וטור הלכות ט"ב.
For the Beit Yosef, ב״י; see footnote 20.
For Hagahot Maimuniyyot, הגהות מיימוני; see footnote 27.
Sefer Mitzvot Gadol, סמ״ג, is also known by its acronym SeMaG for Sefer Mitzvot Gadol. It was written by Moses ben Jacob of Coucy, a thirteenth century French scholar and tosafist. Moses of Coucy was the first French Jew to serve as an itinerant preacher, who wandered from town to town and from country to country trying to inspire Jews to renew their faith in God. He began his work in Spain in 1236 apparently after he received some mystical revelation. He excited people to renew their following of the commandments of tefillin (prayer phylacteries), mezuzah (Shema prayers placed on the doorpost), and ẓiẓit (garment fringes) which they had been lax in observing. He also spoke against a practice that had become common among Jews of Spain, having sexual relations with Gentile women. He stressed the value of the study of Torah and all positive commandments which had declined in Spain along with the allegorization of the Bible as a result of the philisophic writings of Maimonides which had become popular in the thirteenth century. Because of his vast sermonizing he received the name of Moses ha-Darshan, Moses the Sermonizer.
The SeMaG, Sefer Mitzvot Gadol, is Moses of Coucy's most extensive and important work, and it was first published before 1480 probably in Rome and again in Italy in 1547. The work is unique among the rabbinic writings of the period because of its style and arrangement. It contains the essence of the Oral Law, and it is arranged in order of the precepts divided into two parts, the positive and the negative precepts. Coucy based his work on the Mishneh Torah of Maimonides (see footnote 59) and he quoted from it directly on almost every page. He basically added to the words of Maimonides using as his source the Babylonian and Jerusalem Talmuds as well as many midrashim, halakhic and aggadic commentaries on the Bible. He also employed the works of French and German rishonim, early scholars (see footnote 16). Coucy changed the language of the midrashim to fit in with the style of Maimonides. The order to the SeMaG is different than that of the Mishneh Torah and even different than Maimonides' Sefer ha-Mitzvot (see footnote 59) which also lists the 613 commandments in positive and negative precepts because Coucy was not familiar with this work by Maimonides. At the end of his book Coucy included rabbinic precepts so as to instruct the people in the way of the Lord, which had been his original aim. To reach this aim, Coucy also separated those precepts which had practical value from those which were no longer applicable. The work of Moses of Coucy, because of his travels in Spain and his discovery of the works of Maimonides, helped bring Maimonides to the awareness of the French Jewish community. It is ironic that the allegorization of the Bible that Moses of Coucy fought so hard against was the result of the philosophy of Maimonides whom, as a halakhist, Moses of Coucy respected so much.
Moses of Coucy employed the following style in Sefer Mitzvot Gadol: he began with a scriptural verse touching on the subject, he then sighted interpretations of the verse found in the Talmuds and the halakhic midrashim. He then gave explanations based on commentators and halakhic scholars, and finally he summarized the halakhah. He weaved into the discussions aggadic and homiletic aspects, many of which were his own creation that displayed a love of God and his fellow man. The SeMaG became quite a popular and well known work among Jewish scholars for many generations. Isaac of Corbeil who had the title of "Head of the Yeshivot of France" compiled a book that was completely dependent on the SeMaG and he called it Sefer Mitzvot Katan, SeMaK, (see footnote 27), and he made it compulsory daily learning for every Jew. The SeMaG was the most accepted halakhic code among Ashkenazi and Sephardi Jewry until its position was taken over by the Shulḥan Arukh. (For an explanation of the SeMaG and how it fits into the entire picture of codification literature, see the introduction to this thesis).
Israel Moses Ta-Shma, E. J., v. 12, pp. 418-20.
The Tur, on the laws concerning the Ninth Day of the month of Av, טור הלכות ט״ב.
Tishah Be-Av is a fast day which commemorates the destruction of both the first Temple (586 B. C. E.) by the Babylonians and the second Temple (70 C. E.) by the Romans in Jerusalem which traditionally occurred on this date, (M. Ta'anit 4:6). (Actually records show that the major destruction of both Temples was on the tenth of Av but the Talmud proclaimed the Ninth Day of Av as the official day of mourning). It is a national day of mourning for the Jewish people. The rules regarding washing one's feet only if they are dirty (for cleansing purposes) are the same on Tisha Be-Av as they are on Yom Kippur.
The Mishna, loc. cit., also points out other calamities that befell the Jewish people on the Ninth Day of Av. It was on that day that the children of Israel were told they could not enter the Promised Land following their exodus from Egypt. On the Ninth of Av Bethar, the last stronghold of the leaders of the Bar Kokhba revolt was captured in 135 C.E. and exactly one year later the Roman Emperor, Hadrian, established a heathen temple on the site of the Temple in Jerusalem and made the city a pagan city which the Jews were not permitted to enter. The Jews later were expelled from Spain in 1492 on Tishah be-Av. This day then became a symbol for the persecutions and misfortunes of the Jews throughout history.
Fasting on the Ninth Day of Av as a day of mourning might have even been in practice during the second Temple period, and it was certainly part of the Jewish life in mishnaic times. It is a fast like Yom Kippur, from sunset to sunset.
In some places it is customary to eat a boiled egg during the last meal before Tishah be-Av sprinkled with ashes to symbolize mourning. No meat or wine is to be included prior to the fast. It is a day of national fasting and mourning. The laws of fasting are very similar to those of Yom Kippur and the laws of mourning parallel those that apply to one who has just lost a close relative after the burial. Lamentations are read as part of the Evening Service. While studying is prohibited, the Book of Job, curses in Leviticus (26:14-42) Jeremiah 39, and stories in the Talmud on the destruction of Jerusalem (Git. 55b-58a) may be read.
Supposedly Tishah be-Av will eventually again become a day of joy as the Messiah is to be born on this day.
Meir Ydit, E. J., v. 3, pp. 936-40.
For thr Tur, טור; see footnote 23.