Mishnah Taharos 3:4: The equivalent [in volume] of an egg of [impure] foods which one placed in the sun and they shrank, and similarly the equivalent of an egg [in volume] of a dead body, or the equivalent of an egg [in volume] of an animal carcass, or the equivalent of a lentil [in volume] of a vermin, or the equivalent of an olive of pigul [any sacrifice about which the priest bringing it had any invalidating intention], or the equivalent of an olive of remainders [leftover sacrifices left past their designated time, which then become forbidden for eating], or the equivalent of an olive of forbidden fats, [if one placed any of these in the sun and they shrunk to less than their initial measure,] these things [the impure foods, the body, the carcass, and the vermin, all of which were impure] are pure, and these [the final three items on the list], one is not subject to liability on account of them, not for pigul, nor for remainders, nor for [eating] forbidden fats [literally: for impurity]. If one placed them in the rain and they swelled [back to their original full measure], they are impure, and one is subject to liability on account of them for pigul, for remainders, and for [eating] forbidden fats [literally: for impurity].

כַּבֵּיצָה אֳכָלִין שֶׁהִנִּיחָן בַּחַמָּה וְנִתְמַעֲטוּ, וְכֵן כַּזַּיִת מִן הַמֵּת, וְכַזַּיִת מִן הַנְּבֵלָה, וְכָעֲדָשָׁה מִן הַשֶּׁרֶץ, כַּזַּיִת פִּגּוּל, כַּזַּיִת נוֹתָר, כַּזַּיִת חֵלֶב, הֲרֵי אֵלּוּ טְהוֹרִים, וְאֵין חַיָּבִין עֲלֵיהֶן מִשּׁוּם פִּגּוּל, נוֹתָר וְטָמֵא. הִנִּיחָן בַּגְּשָׁמִים וְנִתְפְּחוּ, טְמֵאִין, וְחַיָּבִין עֲלֵיהֶם מִשּׁוּם פִּגּוּל, נוֹתָר וְטָמֵא:

Mishnah Taharos 3:5: All impurities [are determined] as they are found: if items are [found] impure, they are [deemed to have been] impure [at the relevant moment for an object in question]; if they are [found] pure, they are [deemed to have been] pure [at the relevant moment for the object in question]. If they are [found] covered [such as an earthenware vessel which protects its contents from impurity when covered by a tight seal], they are [assumed to have been] covered [at the relevant time, and we do not worry that it may have initially been uncovered in the presence certain impurities, and that its contents are therefore impure]; if they are [found] uncovered, they are [assumed to have been] uncovered [at the relevant time]. A needle found full of rust or broken [and therefore unusable, and thus unable to retain impurity], it is pure [and we do not worry that it came into contact with the object in question before it became invalid, i.e. while it was still impure and therefore able to render the object impure], since all impurities [of items are determined] as they are found.

כָּל הַטֻּמְאוֹת, כִּשְׁעַת מְצִיאָתָן. אִם טְמֵאוֹת, טְמֵאוֹת. וְאִם טְהוֹרוֹת, טְהוֹרוֹת. אִם מְכֻסּוֹת, מְכֻסּוֹת. אִם מְגֻלּוֹת, מְגֻלּוֹת. מַחַט שֶׁנִּמְצֵאת מְלֵאָה חֲלֻדָּה אוֹ שְׁבוּרָה, טְהוֹרָה, שֶׁכָּל הַטֻּמְאוֹת, כִּשְׁעַת מְצִיאָתָן: