מדרש על שמות 3:13

Moses said unto God: Behold, when I come unto the children of Israel and I shall say to them the God of your fathers sent me. What shall I say to them (Exod. 3:13)? Moses pleaded with the Holy One, blessed be He, to divulge His great name to him. He said: If they should ask me, What is His name?, What shall I answer? He answered Moses: Do you desire to know My name? I am known according to My works. When I judge mankind, I am called God; when I take revenge upon the wicked, I am called Hosts; when I consider the sins of man, I am called Almighty God; and when I sit in merciful judgment, I am called Merciful One. My name conforms to My deeds. I urge you, however, to say to them: The God of Abraham, the God of Isaac, and the God of Jacob has sent me unto you; this is My name forever, and this is My memorial unto all generations (ibid., v. 15).

(Exod. 4:21:) THEN THE LORD SAID UNTO MOSES: WHEN YOU GO TO RETURN TO EGYPT. The Holy One showed him the miracles that he was going to do for him. Now he had said to him (Exod. 3:16:): GO AND GATHER THE ELDERS OF ISRAEL,… and afterwards you are going to Pharaoh. Moses said: If they should say TO ME (in Exod. 3:13), WHAT IS HIS NAME, WHAT DO I SAY TO THEM? He said to him: Say to them (in vs. 14): I AM THAT I AM.