סימן קכד סעיף ד

אִם יֵשׁ אָבֵל בָּעִיר, הוֹלֵךְ לְבֵית הַכְּנֶסֶת בַּלַּיְלָה וְגַם בַּיּוֹם עַד שֶׁיִּגְמְרוּ הַקִּינוֹת, וּמֻתָּר לוֹ לַעֲלוֹת לַתּוֹרָה וְלִקְרוֹת הַהַפְטָרָה, שֶׁהֲרֵי כֻּלָּם אֲבֵלִים הֵם.

If there is a mourner in the town, he should go to the synagogue on the night (of Tishah beAv) and also during the day,⁹Other Poskim maintain that during the first three days of mourning, he should not go to the synagogue. Rav Shlomo Kluger ruled that he should not go at night, when only a limited Kinnos is said, but by day, when the majority of Kinnos is said, he is permitted to go. After the three days, however, he may go, even at night. (See Mishnah Berurah 559:24 and also Shaar Hatzion 22) (and stay) until the conclusion of the Kinnos. He is permitted to receive an aliyah and to read the haftarah,¹⁰This rule is not mentioned in Mishnah Berurah. because we all are mourners (on Tishah beAv).

תנא דבי אליהו כל השונה הלכות בכל יום מובטח לו שהוא בן העולם הבא שנאמר הליכות עולם לו אל תקרי הליכות אלא הלכות (נדה ע"ג.)