"For no human can see Me and live" (Exodus 33:20). Rabbi Yochanan said: Had there remained in the cave where Moses and Elijah stood even as much empty space as the eye of a fine sewing needle, they would not have been able to stand in the cave because of the light.
The Cave of Moses and Elijah Filled With Light
Yalkut Shimoni on Torah 396:2
כִּי לֹא יִרְאַנִי הָאָדָם וָחָי. אֲמַר רַבִּי יוֹחָנָן. אִלְמָלֵא נִשְׁתַּיֵּר בַּמְּעָרָה, שֶׁעָמַד בָּהּ מֹשֶׁה וְאֵלִיָּהוּ, כִּמְלֹא נֶקֶב מַחַט סִדְקִית, לֹא הָיוּ יְכוֹלִין לַעֲמֹד בַּמְּעָרָה מִפְּנֵי הָאוֹרָה.