Kiddushin 71a
קידושין ע״א א — ד"ה אָמַר רַב יְהוּדָה אָמַר רַב
Kiddushin 71a:13
The Gemara there records teachings about the divine name, including traditions of hidden pronunciation and transmission. It is a foundational rabbinic source for the guarded nature of God's name.
אָמַר רַב יְהוּדָה אָמַר רַב: שֵׁם בֶּן אַרְבָּעִים וּשְׁתַּיִם אוֹתִיּוֹת אֵין מוֹסְרִין אוֹתוֹ אֶלָּא לְמִי שֶׁצָּנוּעַ וְעָנָיו, וְעוֹמֵד בַּחֲצִי יָמָיו, וְאֵינוֹ כּוֹעֵס, וְאֵינוֹ מִשְׁתַּכֵּר, וְאֵינוֹ מַעֲמִיד עַל מִדּוֹתָיו. וְכׇל הַיּוֹדְעוֹ, וְהַזָּהִיר בּוֹ וְהַמְשַׁמְּרוֹ בְּטׇהֳרָה – אָהוּב לְמַעְלָה, וְנֶחְמָד לְמַטָּה, וְאֵימָתוֹ מוּטֶּלֶת עַל הַבְּרִיּוֹת, וְנוֹחֵל שְׁנֵי עוֹלָמִים – הָעוֹלָם הַזֶּה וְהָעוֹלָם הַבָּא.
Rav Yehuda says that Rav says: The forty-two-letter name of God may be transmitted only to one who is discreet, and humble, and stands at at least half his life, and does not get angry, and does not get drunk, and does not insist upon his rights but is willing to yield. There is no concern that such a person might reveal the name in a fit of anger or drunkenness. And anyone who knows this name and is careful with it and guards it in purity is beloved above and treasured below; and fear of him is cast upon the creatures; and he inherits two worlds, this world and the World-to-Come.