Reference for Niddah 3:1

הַמַּפֶּלֶת חֲתִיכָה, אִם יֵשׁ עִמָּהּ דָּם, טְמֵאָה. וְאִם לָאו, טְהוֹרָה. רַבִּי יְהוּדָה אוֹמֵר, בֵּין כָּךְ וּבֵין כָּךְ, טְמֵאָה:

Regarding a woman who miscarries a piece [of flesh], if there was blood with it, she is impure; it not, she is pure. Rabbi Yehudah says: either way she is impure.

Jastrow