Mishnah Niddah 2:3: What is [considered to be] after some time? As long as it takes for her to descend from the bed and rinse her [nether] face. And afterwards [if she found blood], she [retroactively] renders impurity from that time to that time [twenty-four hours earlier], but she does not render impure the man who had intercourse with her. Rabbi Akiva says: she also renders impure the man who had intercourse with her. And the Sages agree with Rabbi Akiva regarding one who sees a [blood] stain, that she renders impure the man who has intercourse with her [after she saw the stain].

אֵיזֶהוּ אַחַר זְמַן. כְּדֵי שֶׁתֵּרֵד מִן הַמִּטָּה וְתָדִיחַ פָּנֶיהָ. וְאַחַר כָּךְ, מְטַמְּאָה מֵעֵת לְעֵת וְאֵינָהּ מְטַמְּאָה אֶת בּוֹעֲלָהּ. רַבִּי עֲקִיבָא אוֹמֵר, אַף מְטַמְּאָה אֶת בּוֹעֲלָהּ. וּמוֹדִים חֲכָמִים לְרַבִּי עֲקִיבָא בְּרוֹאָה כֶתֶם, שֶׁמְּטַמְּאָה אֶת בּוֹעֲלָהּ:

Mishnah Niddah 2:4: All women are presumed to be pure for their husbands [i.e. husbands may presume that their wives are pure]. Those who return from a journey, their wives are presumed to be pure for them. Beit Shammai says: she requires two checking-cloths [literally: witnesses] for each and every time she has intercourse [i.e. so she can check them the next day], or she must have relations by the light of a candle [i.e. she must use a checking-cloth after intercourse and examine it by candlelight then]. Beit Hillel says: two checking-cloths suffice for her for the whole night.

כָּל הַנָּשִׁים בְּחֶזְקַת טָהֳרָה לְבַעֲלֵיהֶן. הַבָּאִין מִן הַדֶּרֶךְ, נְשֵׁיהֶן לָהֶן בְּחֶזְקַת טָהֳרָה. בֵּית שַׁמַּאי אוֹמְרִים, צְרִיכָה שְׁנֵי עִדִּים עַל כָּל תַּשְׁמִישׁ וְתַשְׁמִישׁ, אוֹ תְשַׁמֵּשׁ לְאוֹר הַנֵּר. בֵּית הִלֵּל אוֹמְרִים, דַּיָּהּ בִּשְׁנֵי עִדִּים כָּל הַלָּיְלָה: