Reference for Tahorot 5:5

שְׁנֵי שְׁבִילִין, אֶחָד טָמֵא וְאֶחָד טָהוֹר, הָלַךְ בְּאַחַד מֵהֶן וְעָשָׂה טָהֳרוֹת, וּבָא חֲבֵרוֹ וְהָלַךְ בַּשֵּׁנִי וְעָשָׂה טָהֳרוֹת, רַבִּי יְהוּדָה אוֹמֵר, אִם נִשְׁאֲלוּ זֶה בִפְנֵי עַצְמוֹ וְזֶה בִפְנֵי עַצְמוֹ, טְהוֹרִין. וְאִם נִשְׁאֲלוּ שְׁנֵיהֶם כְּאֶחָד, טְמֵאִים. רַבִּי יוֹסֵי אוֹמֵר, בֵּין כָּךְ וּבֵין כָּךְ, טְמֵאִים:

Two paths, one impure and one pure, if someone walked down one of them and then prepared pure things, and then his fellow came and walked down the second one and prepared pure things, Rabbi Yehuda says: If each one of them inquired individually [regarding his own purity status], they are both pure, but if they inquired together, they are impure. Rabbi Yose says: in either case they are impure.

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