Exodus 6:12

6:12 But Moses replied to the Lord, “If the Israelites did not listen to me, then how will Pharaoh listen to me, since I speak with difficulty?”

Jeremiah 1:6

1:6 I answered, “Oh, Lord God, I really do not know how to speak well enough for that, for I am too young.”

Acts 7:22

7:22 So Moses was trained in all the wisdom of the Egyptians and was powerful in his words and deeds.