Mishnah Niddah 10:5: If a woman died and a revi'it [a specific unit of volume, a quarter of a log] of blood emerged from her, it renders impurity as a [blood] stain and it renders impurity by overshadowing. Rabbi Yehuda says: it does not render impurity as a stain because it was uprooted [from its source] after she died. But Rabbi Yehuda is in agreement regarding one who died while sitting on a birthing stool and a revi'it of blood emerged from her, that it renders impurity as a [blood] stain. Rabbi Yose says: therefore it does not render impurity by overshadowing [since that is the law regarding blood that emerges from a corpse, but not from a living person].

הָאִשָּׁה שֶׁמֵּתָה וְיָצָא מִמֶּנָּה רְבִיעִית דָּם, מְטַמְּאָה מִשּׁוּם כֶּתֶם, וּמְטַמְּאָה בְאֹהֶל. רַבִּי יְהוּדָה אוֹמֵר, אֵינָהּ מְטַמְּאָה מִשּׁוּם כֶּתֶם, מִפְּנֵי שֶׁנֶּעֱקַר מִשֶּׁמֵּתָה. וּמוֹדֶה רַבִּי יְהוּדָה בְּיוֹשֶׁבֶת עַל מַשְׁבֵּר וּמֵתָה וְיָצָא מִמֶּנָּה רְבִיעִית דָּם, שֶׁהִיא מְטַמְּאָה מִשּׁוּם כֶּתֶם. אָמַר רַבִּי יוֹסֵי, לְפִיכָךְ אֵינָהּ מְטַמְּאָה בְאֹהֶל:

Mishnah Niddah 10:6: Initially they would say: One sitting in pure blood [during the days of purity after the postpartum days of impurity] may pour out water for [rinsing] the Pesach offering [since she does not touch it, nor does she render impure the vessel from which she pours]. They then retracted, saying: with regard to sanctified things she thereby is like one who touched something rendered impure by a corpse, in accordance with Beit Hillel. Beit Shammai say: even [she herself is] like one who was rendered impure by a corpse.

בָּרִאשׁוֹנָה הָיוּ אוֹמְרִים, הַיּוֹשֶׁבֶת עַל דַּם טֹהַר, הָיְתָה מְעָרָה מַיִם לַפֶּסַח. חָזְרוּ לוֹמַר, הֲרֵי הִיא כְמַגַּע טְמֵא מֵת לַקָּדָשִׁים, כְּדִבְרֵי בֵית הִלֵּל. בֵּית שַׁמַּאי אוֹמְרִים, אַף כִּטְמֵא מֵת: