סימן ריט סעיף ב
אִם קָרְאוּ אֶת הָאָבֵל לַעֲלוֹת לַתּוֹרָה, צָרִיךְ לַעֲלוֹת. כִּי אִם הָיָה נִמְנָע, הֲוֵי דָּבָר שֶׁבְּפַרְהֶסְיָא. וְרַבֵּינוּ תָּם הָיוּ קוֹרִין אוֹתוֹ בְּכָל שַׁבָּת לִשְׁלִישִׁי, וְאֵרַע לוֹ אֵבֶל וְלֹא קְרָאוֹ הַחַזָן, וְעָלָה הוּא מֵעַצְמוֹ וְאָמַר, כֵּיוָן שֶׁהֻרְגַּל לִקְרוֹת שְׁלִישִׁי בְּכָל שַׁבָּת, הָרוֹאֶה שֶׁאֵינוֹ עוֹלֶה הַיּוֹם, יֵדַע שֶׁהוּא מֵחֲמַת אֲבֵלוּת, וַהֲוֵי פַרְהֶסְיָא. וְכֵן אִם הַכֹּהֵן הוּא אָבֵל וְאֵין כֹּהֵן אַחֵר בְּבֵית הַכְּנֶסֶת, צְרִיכִין לִקְרוֹתוֹ. אֲבָל יוֹתֵר טוֹב שֶׁיֵצֵא מִבֵּית הַכְּנֶסֶת קֹדֶם הוֹצָאַת סֵפֶר הַתּוֹרָה. וְכֵן אִם יֵשׁ לְאָבֵל בֵּן לָמוּל וְהַמִּנְהָג שֶׁהוּא חִיוּב לַעֲלוֹת לַתּוֹרָה, יִקְרָאוּהוּ. דְּאִם לֹא יִקְרָאוּהוּ, הֲוֵי פַרְהֶסְיָא, וְיוֹתֵר טוֹב שֶׁלֹּא יְהֵא בְּבֵית הַכְנֶסֶת בִּשְׁעַת קְרִיאַת הַתּוֹרָה. (אִשָּׁה שֶׁהִגִּיעַ זְמַנָּה לָלֶכֶת לְבֵית הַכְּנֶסֶת בְּשַׁבָּת שֶׁבִּימֵי אֶבְלָהּ, עַיֵן לְעֵיל סִימָן ריא סָעִיף יא)
If the mourner was called to the reading of the Torah, he must go up, for if he were to refuse, it would constitute a public display of mourning. Rabbeinu Tam used to be called to the Torah to the reading of the third portion every Shabbos; and when he happened to be in mourning and the Chazzan failed to call him, he went up himself. He said that since he had been accustomed to read the third portion every Shabbos, those who would see that he did not go up this day would understand that it was due to his mourning, and this would be a public display of mourning. Also, if a Kohein is a mourner, and there is no other Kohein in the synagogue, they must call him up to the reading of the Torah. However, it is preferable that he leave the synagogue4This is true only if it is the accepted practice for the Kohein to leave in order for a Yisroel to be called up. See Chassam Sofer resp. Yoreh Deah 352. Tashbatz 2:276 states he should not go out, because doing so constitutes public display of mourning. And so the Rabbeinu Tam did not go out either. before the Seifer Torah is taken out of the Aron HaKodesh. Also, if the mourner has a son to be circumcised and it is the custom that he must go up to the Torah reading, they should call him up. For if they do not call him, it constitutes a public display of mourning.5Halachos Ketanos 1:289, Aish Dos resp. 7. The Maharshal responsa 71 says not to call him. But it is preferable that he not be in the synagogue during the reading of the Torah.6Eliyohu Rabba 132:4. (As for a woman whose time has come to go to the synagogue occurs on the Shabbos during her mourning, see chapter 211:11, above.)
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.)