Mishnah Negaim 5:2 :[If] he decided it [to be impure] by its white hair [seen in the Nega], [if] the white hair went away and then the white hair reappeared, and so too [if the hair was replaced with] a healthy patch of skin or an expansion, [whether he decided it by its white hair] initially, at the end of the first week, at the end of the second week, or after it was exempted, behold it returns to its previous status [of impurity]. [If] he decided it [to be impure] by a healthy patch of skin [seen in the Nega], [if] the healthy patch of skin went away and then the healthy patch of skin reappeared, and so too [if the patch was replaced with] white hair or an expansion, [whether he decided it by its healthy patch of skin] initially, at the end of the first week, at the end of the second week, or after it was exempted, behold it returns to its previous status [of impurity]. [If] he decided it [to be impure] by an expansion [of the Nega], [if] the expansion went away and then the expansion reappeared, and so too [if the expansion was replaced with] white hair, [whether he decided it by its expansion] at the end of the first week, at the end of the second week, or after it was exempted, behold it returns to its previous status [of impurity].

הֶחְלִיטוֹ בְשֵׂעָר לָבָן, הָלַךְ שֵׂעָר לָבָן וְחָזַר שֵׂעָר לָבָן, וְכֵן בְּמִחְיָה וּבְפִשְׂיוֹן, בַּתְּחִלָּה וּבְּסוֹף שָׁבוּעַ רִאשׁוֹן, בְּסוֹף שָׁבוּעַ שֵׁנִי, לְאַחַר הַפְּטוּר, הֲרֵי הִיא כְמוֹ שֶׁהָיְתָה. הֶחְלִיטוֹ בְמִחְיָה, וְהָלְכָה הַמִּחְיָה וְחָזְרָה הַמִּחְיָה. וְכֵן בְּשֵׂעָר לָבָן וּבְפִשְׂיוֹן, בַּתְּחִלָּה, בְּסוֹף שָׁבוּעַ רִאשׁוֹן, בְּסוֹף שָׁבוּעַ שֵׁנִי, לְאַחַר הַפְּטוּר, הֲרֵי הִיא כְמוֹ שֶׁהָיְתָה. הֶחְלִיטוֹ בְפִשְׂיוֹן, הָלַךְ הַפִּשְׂיוֹן וְחָזַר הַפִּשְׂיוֹן. וְכֵן בְּשֵׂעָר לָבָן, בְּסוֹף שָׁבוּעַ רִאשׁוֹן, בְּסוֹף שָׁבוּעַ שֵׁנִי, לְאַחַר הַפְּטוּר, הֲרֵי הִיא כְמוֹת שֶׁהָיְתָה:

Mishnah Negaim 5:3: The hair of Pekudah - Akavya ben Mahalal'el declares impure and the Sages declare pure. What is the hair of Pekudah? Someone who had upon him a Baheret with white hair in it, [if] the Baheret disappeared and left white hair in its place, and then returned - Akavya ben Mahalal'el declares it impure and the Sages declare it pure. Rabbi Akiva said: "I agree [with the Sages] in this [case] that it is pure." What is the hair of Pekudah [about which Rabbi Akiva disagrees with the Sages]? Someone who had upon him a Baheret like [the size of] a bean with two [white] hairs in it, and then [the size of] half a bean went from it and left the white hair in the area of the Baheret and [then] returned. They [the Sages] said to him: Just like they discredited Akavya’s words, so too your words will not be established [as law].

שְׂעַר פְּקֻדָּה, עֲקַבְיָא בֶן מַהֲלַלְאֵל מְטַמֵּא, וַחֲכָמִים מְטַהֲרִין. אֵיזֶה הוּא שְׂעַר פְּקֻדָּה, מִי שֶׁהָיְתָה בוֹ בַהֶרֶת וּבָהּ שֵׂעָר לָבָן, הָלְכָה הַבַּהֶרֶת וְהִנִּיחָה לְשֵׂעָר לָבָן בִּמְקוֹמוֹ וְחָזְרָה, עֲקַבְיָא בֶן מַהֲלַלְאֵל מְטַמֵּא, וַחֲכָמִים מְטַהֲרִין. אָמַר רַבִּי עֲקִיבָא, מוֹדֶה אֲנִי בְזֶה שֶׁהוּא טָהוֹר. אֵיזֶה הוּא שְׂעַר פְּקֻדָּה, מִי שֶׁהָיְתָה בוֹ בַהֶרֶת כַּגְּרִיס וּבָהּ שְׁתֵּי שְׂעָרוֹת, וְהָלַךְ הֵימֶנָּה כַחֲצִי גְרִיס וְהִנִּיחוֹ לְשֵׂעָר לָבָן בִּמְקוֹם הַבַּהֶרֶת וְחָזַר. אָמְרוּ לוֹ, כְּשֵׁם שֶׁבִּטְּלוּ אֶת דִּבְרֵי עֲקַבְיָא, אַף דְּבָרֶיךָ אֵינָן מְקֻיָּמִין: