Reference for Niddah 4:4
הַמַּקְשָׁה, נִדָּה. קִשְּׁתָה שְׁלשָׁה יָמִים בְּתוֹךְ אַחַד עָשָׂר יוֹם וְשָׁפְתָה מֵעֵת לְעֵת וְיָלְדָה, הֲרֵי זוֹ יוֹלֶדֶת בְּזוֹב, דִּבְרֵי רַבִּי אֱלִיעֶזֶר. רַבִּי יְהוֹשֻׁעַ אוֹמֵר, לַיְלָה וָיוֹם, כְּלֵילֵי שַׁבָּת וְיוֹמוֹ. שֶׁשָּׁפְתָה מִן הַצַּעַר, וְלֹא מִן הַדָּם:
A woman having difficult labor is [considered to be] a <i>niddah</i> [if she saw blood during her days of <i>niddah</i>]. If she had difficult labor [and saw blood] for three days within the eleven days [of <i>zivah</i>, between <i>niddah</i> periods], and she ceased [having pains] from that time to that time [twenty-four hours later], and she gave birth, she has thereby given birth in a state of <i>zov</i> [i.e. while she was a <i>zavah</i>], according to Rabbi Eliezer. Rabbi Yehoshua says: [she must have ceased having pains for] a night and a day, like the night of Shabbat its day [i.e. for a full night and subsequent day, and not for any twenty-four hour period]. This applies to one who ceased [for that time] from her pain, but not [necessarily] from bleeding.