Parashas Shemos
וַיֹּ֩אמֶר֩ ע֨וֹד אֱלֹהִ֜ים אֶל־מֹשֶׁ֗ה כֹּֽה־תֹאמַר֮ אֶל־בְּנֵ֣י יִשְׂרָאֵל֒ יְהֹוָ֞ה אֱלֹהֵ֣י אֲבֹתֵיכֶ֗ם אֱלֹהֵ֨י אַבְרָהָ֜ם אֱלֹהֵ֥י יִצְחָ֛ק וֵאלֹהֵ֥י יַעֲקֹ֖ב שְׁלָחַ֣נִי אֲלֵיכֶ֑ם זֶה־שְּׁמִ֣י לְעֹלָ֔ם וְזֶ֥ה זִכְרִ֖י לְדֹ֥ר דֹּֽר׃
And God said further to Moses, “Thus shall you speak to the Israelites: GOD [יהוה],jיהוה This divine name (y-h-w-h; traditionally pronounced as Adonai, lit. “[the] Sovereign”) is here associated with the verb hayah “to be.” the God of your fathers—the God of Abraham, the God of Isaac, and the God of Jacob—has sent me to you:This shall be My name forever,This My appellation for all eternity.
Torah Temimah points to TT / Yoma (verified).
זה שמי לעלם — בשעה שהיה הכהן גדול ביום הכפורים מזכיר את השם, לא היו השומעים זזים משם עד שהוא מתעלם מהם, דכתיב זה שמי לעולם – לעלם כתיב.
English: “This is My name forever” — when the High Priest would pronounce the Name on Yom Kippur, the hearers would not move from the place until it became concealed from them, as it is written “this is My name le’olam” — written le’alem.
Custom
Chazal link the Yom Kippur utterance of the Name to the spelling that implies concealment after the moment of revelation.