סימן רי סעיף ה
אָבֵל תּוֹךְ שִׁבְעָה, אֵין לוֹ לְהִתְפַּלֵּל לִפְנֵי הַתֵּבָה אֶלָּא אִם אֵין שָׁם אַחֵר שֶׁיִתְפַּלֵל. אַךְ אִם הוּא אָבֵל עַל אָבִיו אוֹ אִמּוֹ, נוֹהֲגִין שֶׁמִּתְפַּלְּלִין לִפְנֵי הַתֵּבָה, אַף עַל פִּי שֶׁיֶשׁ שָׁם אַחֵר. וּבְשַׁבָּתוֹת וְיָמִים טוֹבִים, נוֹהֲגִין שֶׁאֵינוֹ מִתְפַּלֵל לִפְנֵי הַתֵּבָה כָּל הַשָּׁנָה אֶלָּא בִּדְלֵיכָּא אַחֵר. וְאִם הָיָה דַרְכּוֹ לְהִתְפַּלֵּל לִפְנֵי הַתֵּבָה גַּם קֹדֶם שֶׁנַּעֲשָּה אָבֵל, יֵשׁ לְהַתִּיר בְּכָל עִנְיָן (מֵּאִיר נְתִיבִים סִימָן פ). וְעַיֵּן לְעֵיל סִימָן קכח סָעִיף ח (שעו שפד)
During his seven days of mourning a mourner should not officiate as Chazzan unless there is no one else to lead the prayers. But if he is in mourning for his father or mother, the custom is to permit him to be the Chazzan even if there is someone else capable of doing so. It is customary that a mourner not be the Chazzan on Shabbos and Yom Tov4On days when Lamanetzaiach and Kail Erech Appaim are not said, a mourner should not be the Chazzan, except on the day before Yom Kippur. Biur Halachah 132. On Rosh Chodesh he may be the Chazzan for Shacharis, provided someone else continues with the Hallel. However, the Chayei Adam says that the Gra did not allow a mourner to be the Chazzan at Shacharis on Rosh Chodesh. Mishna Berurah 581:7. A mourner should not be the Chazzan at Shacharis on Chanukah. Mishna Berurah 683:1 A mourner is allowed to be Chazzan at Mincha and Ma’ariv on Chanukah. But not on Chol Hamoed. Mishna Berurah 671:44—Peri Megadim. during his entire year5If he is mourning the loss of a parent, or thirty days if he is mourning the loss of another relative. Mishnah Berurah 581:7. [of mourning] unless there is no one else to do so.6If no one else can read the Megillah as accurately as he, he should read it for everyone. Mishnah Berurah 696:12. If he was accustomed to be the Chazzan even before he became a mourner, he is permitted to do so in any event. See Chapter 128:8 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.)