Mishnah Oholot 17:5: A field in which a grave was lost, and they built a house with an upper story on top of it, if the doorway of the upper story was aligned with the doorway of the house, the upper story is pure, but if not the upper story is impure. Dirt of the Beit Pras and dirt of land outside the land of Israel which came in a vegetable combine [to become impure if their combined size is as large as] the seal of leather sacks says Rabbi Eliezer. But the Sages say [they do not become impure] until there is [the size of] the seal of leather sacks in one place. Rabbi Yehuda says, it once happened that letters came from overseas to the sons of the High Priests with a Se'ah or two Se'ah of seals but they [the Sages] were not concerned about their impurity.

שָׂדֶה שֶׁאָבַד קֶבֶר בְּתוֹכָהּ, וּבָנָה בָהּ בַּיִת וַעֲלִיָּה עַל גַּבָּיו, אִם הָיְתָה פִתְחָהּ שֶׁל עֲלִיָּה מְכֻוָּן כְּנֶגֶד פִּתְחוֹ שֶׁל בַּיִת, עֲלִיָּה טְהוֹרָה. וְאִם לָאו, עֲלִיָּה טְמֵאָה. עֲפַר בֵּית הַפְּרָס וַעֲפַר חוּצָה לָאָרֶץ שֶׁבָּא בְיָרָק, מִצְטָרְפִין כְּחוֹתַם הַמַּרְצוּפִים, דִּבְרֵי רַבִּי אֱלִיעֶזֶר. וַחֲכָמִים אוֹמְרִים, עַד שֶׁיִּהְיֶה בְמָקוֹם אֶחָד כְּחוֹתַם הַמַּרְצוּפִין. אָמַר רַבִּי יְהוּדָה, מַעֲשֶׂה שֶׁהָיוּ אִגְּרוֹת בָּאוֹת מִמְּדִינַת הַיָּם לִבְנֵי כֹהֲנִים גְּדוֹלִים, וְהָיוּ בָהֶם כִּסְאָה וּכְסָאתַיִם חוֹתָמוֹת, וְלֹא חָשׁוּ לָהֶם חֲכָמִים מִשּׁוּם טֻמְאָה:

Mishnah Oholot 18:1: How can one harvest grapes in the Beit Pras [a field in which a grave has been plowed over]? We sprinkle on the person and the vessels and repeat and they can harvest the grapes and take them out of the Beit Pras, and others receive from them and carry to the winepress. If these [people] touched those, they are impure according to the words of the House of Hillel. The House of Shammai say, he holds the sickle with palm tree bark [which cannot become impure] or harvests the grapes with a rock and places them in a basket and take them to the winepress. Rabbi Yossi says, when is this the case? In a vineyard that became the Beit Pras, but if he planted in the Beit Pras, they should be sold in the market.

כֵּיצַד בּוֹצְרִים בֵּית הַפְּרָס. מַזִּים עַל הָאָדָם וְעַל הַכֵּלִים, וְשׁוֹנִים וּבוֹצְרִים וּמוֹצִיאִים חוּץ לְבֵית הַפְּרָס, וַאֲחֵרִים מְקַבְּלִים מֵהֶם וּמוֹלִיכִים לַגָּת. אִם נָגְעוּ אֵלּוּ בָאֵלּוּ, טְמֵאִים, כְּדִבְרֵי בֵית הִלֵּל. בֵּית שַׁמַּאי אוֹמְרִים, אוֹחֵז אֶת הַמַּגָּל בְּסִיב, אוֹ בוֹצֵר בְּצוֹר וְנוֹתֵן לְתוֹךְ הַכְּפִישָׁה וּמוֹלִיךְ לַגָּת. אָמַר רַבִּי יוֹסֵי, בַּמֶּה דְבָרִים אֲמוּרִים, בְּכֶרֶם הַנַּעֲשָׂה בֵית הַפְּרָס. אֲבָל נוֹטֵעַ בֵּית הַפְּרָס, יִמָּכֵר לַשּׁוּק: