Avot1: 11
אַבְטַלְיוֹן אוֹמֵר: חֲכָמִים, הִזָּהֲרוּ בְּדִבְרֵיכֶם, שֶׁמָּא תָחוֹבוּ חוֹבַת גָּלוּת וְתִגְלוּ לִמְקוֹם מַיִם הָרָעִים, וְיִשְׁתּוּ הַתַּלְמִידִים הַבָּאִים אַחֲרֵיכֶם וְיָמוּתוּ, וְנִמְצָא שֵׁם שָׁמַיִם מִתְחַלֵּל.
Avtalyon says: Sages, be cautious with your words, for perhaps you will become liable to the punishment of exile, and you will be exiled to a place of evil waters, and the students who come after you will drink [from these waters] and will die, and it will emerge that the Name of Heaven will be desecrated.