Exodus 6:28-30; Exodus 6:7

28 Now when the LORD spoke to Moses in Egypt, 29 he said to him, "I am the LORD. Tell Pharaoh king of Egypt everything I tell you." 30 But Moses said to the LORD, "Since I speak with faltering lips, why would Pharaoh listen to me?"
7 I will take you as my own people, and I will be your God. Then you will know that I am the LORD your God, who brought you out from under the yoke of the Egyptians.