Mishnah Negaim 5:4: Any doubt regarding Negaim initially is considered pure, until it has been obligated in impurity. Once it has been obligated in impurity, its doubt is considered impure. How so? Two who came to a priest, one with a Baheret like [the size of] a bean, and one like a Sela. At the end of the week [of quarantine], one is like a Sela and the other is like a Sela, but its unclear which one expanded. [This law applies] whether it was one person [with two Negaim] or two people, it is considered pure. Rabbi Akiva says: Regarding one person, it is impure but regarding two people, it is pure.

כָּל סְפֵק נְגָעִים בַּתְּחִלָּה טָהוֹר, עַד שֶׁלֹּא נִזְקַק לְטֻמְאָה. מִשֶּׁנִּזְקַק לְטֻמְאָה, סְפֵקוֹ טָמֵא. כֵּיצַד. שְׁנַיִם שֶׁבָּאוּ אֵצֶל כֹּהֵן, בָּזֶה בַהֶרֶת כַּגְּרִיס וּבָזֶה כַּסֶּלַע, בְּסוֹף שָׁבוּעַ בָּזֶה כַּסֶּלַע וּבָזֶה כַּסֶּלַע, וְאֵינוֹ יָדוּעַ בְּאֵיזֶה מֵהֶן פָּשָׂה, בֵּין בְּאִישׁ אֶחָד בֵּין בִּשְׁנֵי אֲנָשִׁים, טָהוֹר. רַבִּי עֲקִיבָא אוֹמֵר, בְּאִישׁ אֶחָד, טָמֵא. וּבִשְׁנֵי אֲנָשִׁים, טָהוֹר:

Mishnah Negaim 5:5: Once [the Nega] has been obligated in impurity, its doubt is considered impure. How so? If two [people] came to a priest, one with a Baheret like [the size of] a bean, and one like a Sela. At the end of the week [of quarantine], if one is like [the size of] a Sela and more and the other is like [the size of] a Sela and more, both of them are impure. Even if [their Negaim] return to both be like [the size of] a Sela, they are impure until they return to be like [the size of] a bean. This is as they said: Once it has been obligated in impurity, its doubt is considered impure.

מִשֶּׁנִּזְקַק לְטֻמְאָה, סְפֵקוֹ טָמֵא. כֵּיצַד. שְׁנַיִם שֶׁבָּאוּ אֵצֶל כֹּהֵן, בָּזֶה בַהֶרֶת כַּגְּרִיס וּבָזֶה כַּסֶּלַע, בְּסוֹף שָׁבוּעַ בָּזֶה כַּסֶּלַע וָעוֹד וּבָזֶה כַּסֶּלַע וָעוֹד, שְׁנֵיהֶן טְמֵאִין. אַף עַל פִּי שֶׁחָזְרוּ לִהְיוֹת כַּסֶּלַע וְכַסֶּלַע, שְׁנֵיהֶן טְמֵאִין, עַד שֶׁיַּחְזְרוּ לִהְיוֹת כַּגְּרִיס. זֶה הוּא שֶׁאָמְרוּ, מִשֶּׁנִּזְקַק לְטֻמְאָה, סְפֵקוֹ טָמֵא: