סימן רכ סעיף ג
אִם חָל אֶחָד מִימֵי הָאֲבֵלוּת חוּץ מִיּוֹם הַשְּׁבִיעִי בְּעֶרֶב הָרֶגֶל, יֵשׁ מַתִּירִין לְכַבֵּס כְּסוּתוֹ, וְלֹא יִלְבָּשֶׁנָּה עַד הַלַּיְלָה, כֵּיוָן דְּהָרֶגֶל יְבַטֵּל גְּזֵרַת שִׁבְעָה. וְטוֹב לִזָּהֵר מִלְּכַבֵּס עַד לְאַחַר חֲצוֹת, כְּדֵי שֶׁיִהְיֶה נִכָּר שֶׁמִּפְנֵי הָרֶגֶל הוּא מְכַבֵּס. וְלִרְחוֹץ, אָסוּר עַד הַלָּיְלָה. וְיֵשׁ מַתִּירִין לִרְחוֹץ אַחַר תְּפִלַּת מִנְחָה סָמוּךְ לַחֲשֵׁכָה. וְהֵיכָא דְנָהוּג, נָהוּג. וּבְגִלּוּחַ, לְכֻלֵּי עָלְמָא, אָסוּר.
If one of the days of mourning, except the seventh day, occurs on the eve of a Festival, since the Festival will cancel the seven-day mourning period, some Poskim permit him to wash his clothes, provided he does not wear them until nightfall. It is best to take care not to wash them until the afternoon,3The Kitzur Shulchan Aruch in the following paragraph says not to wash until near the evening. This is also the ruling of the Mishnah Berurah 548:37. so that it is evident that he is washing them on account of the Festival. He is forbidden to bathe until nightfall, but some Poskim permit bathing4Only bathing, but all other laws of mourning are observed until nightfall. Mishna Berurah 548:39. after the Minchah service,5Only after he already prayed the Minchah service. Mogein Avraham. Even then, he is permitted only near twilight. Yeshuos Yaakov, Mishnah Berurah 548:40. close to nightfall. In places where this custom prevails one may follow it. With regard to having his hair cut, all Poskim agree that it is forbidden.
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.)