סימן קנד סעיף ה
כָּל אִשָּׁה שֶׁיֵשׁ לָהּ וֶסֶת קָבוּעַ, הֲרֵי זוֹ שֶׁלֹּא בִּשְׁעַת וֶסְתָּהּ בְּחֶזְקַת טְהוֹרָה, וּבַעְלָהּ בָּא עָלֶיהָ, וְאֵינוֹ צָרִיךְ לִשְׁאֹל אוֹתָהּ כְּלוּם. וַאֲפִלּוּ הִיא יְשֵׁנָה קְצָת, יָכוֹל לָבוֹא עָלֶיהָ, וְאֵינָהּ צְרִיכָה בְדִיקָה לֹא לִפְנֵי תַּשְׁמִישׁ וְלֹא לְאַחַר תַּשְׁמִישׁ. וְאַדְּרַבָּא, אֵין לָהּ לִבְדֹּק אֶת עַצְמָהּ בִּפְנֵי בַעְלָהּ, שֶׁלֹּא יְהֵא לִבּוֹ נוֹקְפוֹ לַחְשֹׁב מִסְּתָּמָא הִרְגִּישָׁה, שֶׁאִם לֹא הִרְגִישָׁה לֹא הָיְתָה בוֹדֶקֶת. וְלָכֵן אִם תִּבְדֹּק בְּפָנָיו לִפְנֵי תַּשְׁמִישׁ, אִכָּא לְמֵיחָשׁ, שֶׁמָּא מֵחֲמַת שֶיִהְיֶה לִבּוֹ נוֹקְפוֹ יִפְרוֹשׁ אֶת עַצְמוֹ מִמֶּנָה. וְאִם תִּבְדֹּק בְפָנָיו לְאַחַר תַּשְׁמִישׁ, אִכָּא לְמֵיחָש, שֶׁמָּא יְהֵא לִבּוֹ נוֹקְפוֹ לַחְשֹׁב, דְּמִסְּתָמָא הִרְגִּישָׁה בִּשְעַת תַּשְׁמִישׁ, וְיִפְרוֹשׁ אֶת עַצְמוֹ בְפַעַם אַחֶרֶת. וְעַל כֵּן לֹא תִבְדֹּק בִּפְנֵי בַעְלָהּ. אֲבָל שֶׁלֹּא בִפְנֵי בַעְלָהּ, כָּל אִשָּׁה שֶׁמַּרְבֶּה לִבְדֹּק אֶת עַצְמָהּ, הֲרֵי זוֹ מְשֻׁבָּחַת.
A woman whose periods are regular, is at all other times presumed to be menstrually clean, and her husband may have marital relations with her, and does not have to inquire about her status. Even if she is partly asleep he may have marital relations with her, and she does not need to examine herself, either before marital relations or afterwards. On the contrary, she should not examine herself in the presence of her husband,4Not necessarily his presence but rather his knowledge. so that he will not be apprehensive, thinking she probably felt something, for if she did not feel something she would not have examined herself. Therefore if she examines herself in his presence, before having marital relations, there is cause for concern, that perhaps because of his apprehension he might keep away from her.5And thus neglect the mitzvah of propagation. (L’vush 186) And if she examines herself in his presence after having marital relations, there is cause for concern that perhaps he will be apprehensive, thinking that she probably felt something while having marital relations, and will keep away from her the next time. Therefore, she should not examine herself in her husband's presence. But if not in her husband's presence, the more a woman examines herself, the more praiseworthy she is.
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.)