Exodus 7:1-8 NKJV

1 So the Lord said to Moses: "See, I have made you as God to Pharaoh, and Aaron your brother shall be your prophet.
2 You shall speak all that I command you. And Aaron your brother shall speak to Pharaoh to send the children of Israel out of his land.
3 And I will harden Pharaoh's heart, and multiply My signs and My wonders in the land of Egypt.
4 But Pharaoh will not heed you, so that I may lay My hand on Egypt and bring My armies and My people, the children of Israel, out of the land of Egypt by great judgments.
5 And the Egyptians shall know that I am the Lord, when I stretch out My hand on Egypt and bring out the children of Israel from among them."
6 Then Moses and Aaron did so; just as the Lord commanded them, so they did.
7 And Moses was eighty years old and Aaron eighty-three years old when they spoke to Pharaoh.
8 Then the Lord spoke to Moses and Aaron, saying,