Mishnah Niddah 4:3: Regarding the blood of a gentile woman, and the pure blood of a leprous woman [i.e. during her postpartum days of purity], Beit Shammai consider it pure; and Beit Hillel say: it is like her spit or her urine [i.e. it renders impurity only while damp]. Regarding the blood of a woman who gave birth and did not immerse, Beit Shammai say: it is like her spit or her urine. And Beit Hillel say: it renders impurity when damp or dry. And they are in agreement that if she gave birth while while she was a zavah [a female who has certain types of atypical genital discharges, distinct from her menses, which render her impure], that she [i.e. her blood] renders impurity when damp or dry.

דַּם נָכְרִית וְדַם טָהֳרָה שֶׁל מְצֹרַעַת, בֵּית שַׁמַּאי מְטַהֲרִים. וּבֵית הִלֵּל אוֹמְרִים, כְּרֻקָּהּ וּכְמֵימֵי רַגְלֶיהָ. דַּם יוֹלֶדֶת שֶׁלֹּא טָבְלָה, בֵּית שַׁמַּאי אוֹמְרִים, כְּרֻקָּהּ וּכְמֵימֵי רַגְלֶיהָ. וּבֵית הִלֵּל אוֹמְרִים, מְטַמֵּא לַח וְיָבֵשׁ. וּמוֹדִים בְּיוֹלֶדֶת בְּזוֹב, שֶׁהִיא מְטַמְּאָה לַח וְיָבֵשׁ:

Mishnah Niddah 4:4: A woman having difficult labor is [considered to be] a niddah [if she saw blood during her days of niddah]. If she had difficult labor [and saw blood] for three days within the eleven days [of zivah, between niddah 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 while she was a zavah, 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.

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: