Exodus 6:29-7:7

And the Lord said to Moses, "I am the Lord; speak to Pharaoh king of Egypt all that I will tell you," Moses appealed to the Lord, saying, "See, I am of impeded speech; how then should Pharaoh heed me!" The Lord replied to Moses, "See, I place you in the role of God to Pharaoh, with your brother Aaron as your prophet. You shall repeat all that I command you, and your brother Aaron shall speak to Pharaoh to let the Israelites depart from his land. But I will harden Pharaoh's heart, that I may multiply My signs and marvels in the land of Egypt. When Pharaoh does not heed you, I will lay My hand upon Egypt and deliver My ranks, My people the Israelites, from the land of Egypt with extraordinary chastisements. And the Egyptians shall know that I am the Lord, when I stretch out My hand over Egypt and bring out the Israelites from their midst." This Moses and Aaron did; as the Lord commanded them, so they did. Moses was eighty years old and Aaron eighty-three, when they made their demand on Pharaoh.