recovered from “Taanit 31b”
Taanit
תענית ל׳ א — ד"ה תָּנוּ רַבָּנַן
Taanit 30a:10
On the Ninth of Av, one is prohibited from reading Torah, Prophets, Writings, Mishna, Gemara, midrash, and collections of halakhot and aggadot; however, one may read from unfamiliar passages of Tanach or Talmud, from Lamentations, Job, and the prophecies of doom in Jeremiah, while schoolchildren cease their studies altogether.
תָּנוּ רַבָּנַן: כׇּל מִצְוֹת הַנּוֹהֲגוֹת בְּאָבֵל — נוֹהֲגוֹת בְּתִשְׁעָה בְּאָב; אָסוּר בַּאֲכִילָה וּבִשְׁתִיָּה, וּבְסִיכָה, וּבִנְעִילַת הַסַּנְדָּל, וּבְתַשְׁמִישׁ הַמִּטָּה. וְאָסוּר לִקְרוֹת בַּתּוֹרָה בַּנְּבִיאִים וּבַכְּתוּבִים, וְלִשְׁנוֹת בַּמִּשְׁנָה בַּתַּלְמוּד וּבַמִּדְרָשׁ וּבָהֲלָכוֹת וּבָאַגָּדוֹת. אֲבָל קוֹרֵא הוּא בִּמְקוֹם שֶׁאֵינוֹ רָגִיל לִקְרוֹת, וְשׁוֹנֶה בִּמְקוֹם שֶׁאֵינוֹ רָגִיל לִשְׁנוֹת, וְקוֹרֵא בְּקִינוֹת בְּאִיּוֹב, וּבִדְבָרִים הָרָעִים שֶׁבְּיִרְמְיָה. וְתִינוֹקוֹת שֶׁל בֵּית רַבָּן בְּטֵלִין, מִשּׁוּם שֶׁנֶּאֱמַר: ״פִּקּוּדֵי ה׳ יְשָׁרִים מְשַׂמְּחֵי לֵב״.
The Sages taught: All mitzvot practiced by a mourner are likewise practiced on the Ninth of Av: It is prohibited to engage in eating, and in drinking, and in smearing oil on one’s body, and in wearing shoes, and in conjugal relations. It is prohibited to read from the Torah, from the Prophets, and from the Writings, or to study from the Mishna, from the Gemara, and from midrash, and from collections of halakhot, and from collections of aggadot. However, one may read from a place in the Bible that he is unaccustomed to reading, as it will be difficult for him and he will not derive pleasure from it, and he may likewise study from a place of the Talmud that he is unaccustomed to studying. And one may read from the book of Lamentations; from the book of Job; and from the evil matters in Jeremiah, i.e., his prophecies of doom. And schoolchildren interrupt their studies for the day because it is stated: “The precepts of the Lord are right, rejoicing the heart” (Psalms 19:9).