Mishnah Niddah 2:1: Every hand that examines frequently, regarding women, this is praiseworthy; and regarding men, it should be cut off. Regarding a deaf woman, a shotah, a blind woman, or a woman whose cognition has been impaired, if they have able-minded women [to care for them], they prepare them [i.e. help them check themselves and immerse for purity], and they may then eat terumah [a portion of a crop given to the priests which becomes designated as such upon separation, and can only be consumed by priests or their household, and which one is forbidden to render impure]. It is the way of the daughters of Israel to have intercourse using two checking-cloths [literally: witnesses], one for him, and one for her. The modest ones prepare a third, to prepare herself [literally: the house, before intercourse].

כָּל הַיָּד הַמַּרְבָּה לִבְדֹּק בְּנָשִׁים, מְשֻׁבַּחַת. וּבַאֲנָשִׁים, תִּקָּצֵץ. הַחֵרֶשֶׁת וְהַשּׁוֹטָה וְהַסּוּמָא וְשֶׁנִּטְרְפָה דַעְתָּהּ, אִם יֶשׁ לָהֶן פִּקְחוֹת, מְתַקְּנוֹת אוֹתָן וְהֵן אוֹכְלוֹת בַּתְּרוּמָה. דֶּרֶךְ בְּנוֹת יִשְׂרָאֵל, מְשַׁמְּשׁוֹת בִּשְׁנֵי עִדִּים, אֶחָד לוֹ וְאֶחָד לָהּ. הַצְּנוּעוֹת מְתַקְּנוֹת לָהֶן שְׁלִישִׁי, לְתַקֵּן אֶת הַבָּיִת:

Mishnah Niddah 2:2: If [blood was] found on his [checking-cloth], they [the woman and her husband] are both impure, and are liable to bring a sacrifice. If it is found on hers immediately [after intercourse], they are impure, and are liable to bring a sacrifice. If it is found on hers after some time, they are impure as a matter of uncertainty, and they are exempt from bringing a sacrifice.

נִמְצָא עַל שֶׁלּוֹ, טְמֵאִין וְחַיָּבִין קָרְבָּן. נִמְצָא עַל שֶׁלָּהּ אוֹתְיוֹם, טְמֵאִין וְחַיָּבִין קָרְבָּן. נִמְצָא עַל שֶׁלָּהּ לְאַחַר זְמַן, טְמֵאִים מִסָּפֵק וּפְטוּרִים מִן הַקָּרְבָּן: