Ta'anit 29a
תענית כ״ט א — ד"ה וּכְתִיב
Taanit 29a:7
The Gemara establishes that the ninth of Av is a day of calamity and uses the language of recurring misfortune on that date. It frames the day as one of grief, which underlies the special liturgical response of Nachem.
וּכְתִיב: ״וַתִּשָּׂא כׇּל הָעֵדָה וַיִּתְּנוּ אֶת קוֹלָם וַיִּבְכּוּ הָעָם בַּלַּיְלָה הַהוּא״, אָמַר רַבָּה אָמַר רַבִּי יוֹחָנָן: אוֹתוֹ לַיְלָה לֵיל תִּשְׁעָה בְּאָב הָיָה. אָמַר לָהֶם הַקָּדוֹשׁ בָּרוּךְ הוּא: אַתֶּם בְּכִיתֶם בְּכִיָּה שֶׁל חִנָּם — וַאֲנִי קוֹבֵעַ לָכֶם בְּכִיָּה לְדוֹרוֹת. וּתְשִׁיעִי סָמוּךְ לַחֲשֵׁיכָה הֵצִיתוּ בּוֹ אֶת הָאוּר, וְהָיָה דּוֹלֵק וְהוֹלֵךְ כׇּל הַיּוֹם כּוּלּוֹ, שֶׁנֶּאֱמַר: ״אוֹי לָנוּ כִּי פָנָה הַיּוֹם כִּי יִנָּטוּ צִלְלֵי עָרֶב״. וְהַיְינוּ דְּאָמַר רַבִּי יוֹחָנָן: אִלְמָלֵי הָיִיתִי בְּאוֹתוֹ הַדּוֹר לֹא קְבַעְתִּיו אֶלָּא בָּעֲשִׂירִי, מִפְּנֵי שֶׁרוּבּוֹ שֶׁל הֵיכָל בּוֹ נִשְׂרַף. וְרַבָּנַן — אַתְחַלְתָּא דְפוּרְעֲנוּתָא עֲדִיפָא.
And it is further written: “And all the congregation lifted up their voice and cried and the people wept that night” (Numbers 14:1). Rabba said that Rabbi Yoḥanan said: That night was the night of the Ninth of Av. The Holy One, Blessed be He, said to them: You wept needlessly that night, and I will therefore establish for you a true tragedy over which there will be weeping in future generations. And on the ninth, adjacent to nightfall, they set fire to it, and it continuously burned the entire day, as it is stated: “Woe unto us, for the day has declined, for the shadows of the evening are stretched out” (Jeremiah 6:4). This verse is interpreted as a prophecy about the evening when the Temple was burned. And this is what Rabbi Yoḥanan meant when he said: Had I been alive in that generation, I would have established the fast only on the tenth of Av because most of the Sanctuary was burned on that day. And the Sages, who established the fast on the ninth, how do they respond to that comment? They maintain that it is preferable to mark the beginning of the tragedy.