אורח חיים תקע״גOrach Chayim 573

Se’if 1א׳

הִלְכְתָא בָּטְלָה מְגִלַּת תַּעֲנִית, וְכָל הַיָּמִים הַכְּתוּבִים בָּהּ מֻתָּר לְהִתְעַנּוֹת בָּהֶם וְכָל שֶׁכֵּן לִפְנֵיהֶם וּלְאַחֲרֵיהֶם, חוּץ מֵחֲנֻכָּה וּפוּרִים שֶׁאָסוּר לְהִתְעַנּוֹת בָּהֶם בְּעַצְמָם, אֲבָל לִפְנֵיהֶם וּלְאַחֲרֵיהֶם מֻתָּר; וְכֵן שַׁבָּתוֹת וְיָמִים טוֹבִים וְרָאשֵׁי חֳדָשִׁים מֻתָּרִים לִפְנֵיהֶם וּלְאַחֲרֵיהֶם. הַגָּה: מִי שֶׁיֵּשׁ לוֹ נִשּׂוּאִין בַּחֲנֻכָּה אֵין לוֹ לְהִתְעַנּוֹת, אֲבָל אִם יֵשׁ לוֹ נִשּׂוּאִין בְּנִיסָן מִתְעַנֶּה בְּיוֹם חֻפָּתוֹ, אֲפִלּוּ בְּרֹאשׁ חֹדֶשׁ נִיסָן, מִפְּנֵי שֶׁהוּא אֶחָד מִן הַיָּמִים שֶׁמִּתְעַנִּים בָּהֶם, כְּדִלְקַמָּן סוֹף סִימָן תק"פ (הַגָּהוֹת מִנְהָגִים וְלִקוּטֵי מהר"ש).

The halachah is that Megillat Taanit, the scroll of the days on which there is no fasting, has been annulled, and on all the days written in it it is permitted to fast, and all the more so before them and after them — except for Chanukah and Purim, on which it is forbidden to fast on the days themselves, but before them and after them it is permitted; and likewise Sabbaths and festival days and New Moons — the days before them and after them are permitted. Hagah [Rema]: One who has his wedding on Chanukah should not fast; but if he has his wedding in Nisan, he fasts on his wedding day, even on the New Moon of Nisan, because it is one of the days on which people fast, as below, at the end of siman 580 (Hagahot Minhagim and Likkutei Maharash).