Êxodo 33:20 Midrash: Otzar Midrashim, Shemot Rabbah, Ein Yaakov (Glick Edition) & Bamidbar Rabbah

"Seraphim were standing above Him; each one had six wings" (Isaiah 6:2) and it is written "And each one had four faces and four wings" (Ezekiel 1:6). You find Isaiah saw when the Temple stood and Israel was inside it, and saw them with six wings. But Ezekiel, after it was destroyed and Israel exiled from it, he saw them with four. And why did Isaiah see six for each seraph? With two he covers his face so as not to gaze upon the Divine Presence, as it says "For man cannot see Me [and live]" (Exodus 33:20) - even the angels about whom it says "and the likeness of their faces was human faces" (Ezekiel 1:10), with two he covers his legs - these are their feet which are like a calf's hoof, so they will not mention the sins of your fathers [with the calf], and with two he flies, for with these they praise the Omnipresent - behold six. But after the Temple was destroyed, they came to praise before the Holy One Blessed Be He. He takes hold of them and says "My house lies in ruins, My children are exiled - and you seek to praise before me?" Therefore Ezekiel saw four, and Isaiah saw six.

“He said: I am the God of your father, the God of Abraham, the God of Isaac, and the God of Jacob. Moses hid his face, for he was afraid of looking at God” (Exodus 3:6).
“He said: I am the God of your father” – that is what is written: “A fool [peti] believes everything” (Proverbs 14:15). What is a peti? It is a lad, as in Arabia they call a lad petaya. Alternatively, peti is nothing but an expression of seduction, as it is stated: “If a man seduces [yefateh] a woman” (Exodus 22:15).
Rabbi Yehoshua Ha-Kohen bar Neḥemya said: At the moment that The Holy One blessed be He appeared to Moses, Moses was a novice at prophecy. The Holy One blessed be He said: ‘If I appear to him in loud voice, I will terrify him; in soft voice, he will take prophecy lightly.’ What did He do? He appeared to him with the voice of his father. Moses said: ‘Here I am; what does Abba¹The Aramaic term by which Jews to this day refer to their fathers. want?’ The Holy One blessed be He said: ‘I am not your father [Amram], but rather the God of your father. I have come to you with inducements so you will not be afraid.’ “The God of Abraham, the God of Isaac, and the God of Jacob” – Moses was joyful and said: ‘Abba is enumerated with the patriarchs. Moreover, he is greater, as he was mentioned first.’²In the verse, God introduces himself as “the God of your father,” and then as “the God of Abraham, the God of Isaac, and the God of Jacob.”
“Moses hid his face” – he said: ‘The God of my father is standing here and I am not hiding my face?’ Rabbi Yehoshua ben Korḥa and Rabbi Hoshaya, one of them says: Moses did not act properly when he hid his face, as had he not hidden his face, The Holy One blessed be He would have revealed to him what is above, what is below, what was, and what is destined to be. Ultimately, he requested to see, as it is stated: “Please show me Your glory” (Exodus 33:18). The Holy One blessed be He said to Moses: ‘I came to appear to you, and you hid your face. Now I say to you: “For man will not see Me and live” (Exodus 33:20); when I wanted, you did not want.’
Rabbi Yehoshua of Sikhnin said in the name of Rabbi Levi: Nevertheless, He showed him.³Even though according to the previous opinion, hiding his face was inappropriate, God showed him the three mysteries mentioned above. As reward for “Moses hid his face” – “the Lord spoke to Moses face to face” (Exodus 33:11); as reward for “For he was afraid,” – “they were afraid to approach him (Exodus 34:30); as reward for “of looking [mehabit]” – “and the likeness of the Lord he beholds [yabit]” (Numbers 12:8).
Rabbi Hoshaya the Great said: He acted properly when he hid his face. The Holy One blessed be He said to him: ‘I came to reveal My face to you, and you honored Me and hid your face; by your life, you are destined to be with Me on the mountain for forty days and forty nights, without eating and without drinking, and you are destined to enjoy the aura of the Divine Presence, as it is stated: “Moses did not know that the skin of his face glowed” (Exodus 34:29). However, Nadav and Avihu uncovered their heads and feasted their eyes on the aura of the Divine Presence, as it is stated: “Against the nobles of the children of Israel He did not extend His hand” (Exodus 24:11), and they did not receive punishment for what they did.

(Fol. 49b) We are taught that Ben Azai says: "I found a secret scroll wherein it was written that a certain man was a Mamzer. It was also written there that the Mishnath of R. Eliezer b. Jacob is only a Kab (little in quantity), but well sifted. It was also written there that M'nashe executed Isaiah (the prophet)." Raba said: "He was tried before a court (of false prophets) where he was executed. He was asked: 'Moses thy master said (Ex. 33, 20) For no man can see me and live, and you said (Is. 6, 1) I saw the Lord sitting upon a high and exalted throne. Moses your master said (Deut. 4, 7) Who hath God so nigh unto it, as is the Lord our God at all times that we call upon Him, and you said (Is. 55, 6) seek ye the Lord, while He may be found. Moses your master said (Ex. 23, 26) The number of thy days will I make full, and you said (Is. 38, 5) I will add unto thy days fifteen years.' Isaiah then said to himself: I am quite sure that even should I offer him any explanation he will not accept it. If so, then why should I offer it altogether since it would merely cause him to commit [his crime] wilfully? Thereupon he uttered the Tetragrammaton and was swallowed up by a cedar tree. They brought the cedar and sawed it through, and when the saw reached Isaiah's mouth he died, because [of the sin he committed with his mouth when] he said (Is. 6, 5) "And in the midst of a people of unclean lips do I dwell."