Talmud for Eduyot 1:3
הִלֵּל אוֹמֵר, מְלֹא הִין מַיִם שְׁאוּבִין פּוֹסְלִין אֶת הַמִּקְוֶה, אֶלָּא שֶׁאָדָם חַיָּב לוֹמַר בִּלְשׁוֹן רַבּוֹ. וְשַׁמַּאי אוֹמֵר, תִּשְׁעָה קַבִּין. וַחֲכָמִים אוֹמְרִים, לֹא כְדִבְרֵי זֶה וְלֹא כְדִבְרֵי זֶה, אֶלָּא עַד שֶׁבָּאוּ שְׁנֵי גַרְדִּיִּים מִשַּׁעַר הָאַשְׁפּוֹת שֶׁבִּירוּשָׁלַיִם וְהֵעִידוּ מִשּׁוּם שְׁמַעְיָה וְאַבְטַלְיוֹן, שְׁלֹשֶׁת לֻגִּין מַיִם שְׁאוּבִין פּוֹסְלִין אֶת הַמִּקְוֶה, וְקִיְּמוּ חֲכָמִים אֶת דִּבְרֵיהֶם:
Hillel says a whole hin [twelve logs] of drawn water invalidates a mikveh [if they fall into it before its shiur (its minimum amount of non-drawn water) has been completed. But after it has been completed, even if he threw into it all the drawn water in the world, it is not invalidated.] One must use the terminology of his teacher [i.e., "hin" is not Mishnah terminology but Torah terminology. But this is what he heard from his teachers, Shemayah and Avtalyon. And the Rambam received it from his father, of blessed memory, that Shemayah and Avtalyon, being righteous converts (gerei tzedek) could not pronounce "hin" and said "in" instead, (like [many] people today, who cannot enunciate aleph, cheth, heh, and ayin), so that Hillel also said "in," as his teachers, the gerei tzedek, Shemayah and Avtalyon did.] Shammai says nine kavin. And the sages say: Neither like the one nor like the other; but until there came two weavers from the Dung Gate in Jerusalem and testified in the name of Shemayah and Avtalyon that three logs of drawn water invalidate the mikveh, and the sages substantiated their words. ["the Dung Gate": The Tanna mentioned their occupation and their locality to teach that one should not keep himself from the house of study. For there is no trade more menial than that of a weaver, who is not appointed a king or a high-priest. And there is no gate in Jerusalem inferior to the Dung Gate, and yet, they outweighed in their testimony all the sages of Israel.]