סימן קנה סעיף ב

יֵש אוֹמְרִים, דְּעוֹנָה זוֹ שֶׁהוּא צָרִיךְ לִפְרוֹשׁ אֶת עַצְמוֹ, זוֹהִי עוֹנָה שֶׁלִפְנֵי הָעוֹנָה שֶׁהַוֶּסֶת בָּהּ, דְּהַיְנוּ אִם וֶסְתָּהּ בַּלַיְלָה, אֲסוּרָה גַּם כָּל הַיּוֹם שֶׁלְּפָנֶיהָ. וְאִם וֶסְתָּה בַּיּוֹם, אֲסוּרָה גַּם כָּל הַלַּיְלָה שֶׁלְּפָנֶיהָ. וְכֵן יֵשׁ לִנְהֹג. וְאַךְ כְּשֶׁהוּא יוֹצֵא לַדֶּרֶךְ, אוֹ שֶׁהוּא בָא מִן הַדֶּרֶךְ, אוֹ שֶׁחָלָה טְבִילָתָהּ בַּלַיְלָה שֶׁלִּפְנֵי עוֹנַת הַוֶּסֶת, לֹא יַחְמִיר.

Some authorities⁷Ohr Zaruah. say that this onah during which you must separate (from her), is the onah prior to the onah during which she expects her period. For instance, if she expects her period at night, she is also forbidden the entire day before. If she expects her period by day, she is also forbidden the entire night before. And this is the proper course to follow.⁸Toras Hashlomim, Placey, Chochmas Adam, Maharsham 3:258, and Chazon Ish rule that one may be lenient. With regard to other kinds of intimacies, it would seem that even the Ohr Zaruah permits them. However, if you are setting out on a journey, or you have just returned from one, or if she has performed the ritual immersion⁹In these circumstances you are obligated to visit her. on the night preceding her expected period, you should not heed the stricter opinion.

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.)