Exodus 7:1-9

Then the LORD said to Moses, “Now hear this: I make you as God to Pharaoh [to declare My will and purpose to him]; and your brother Aaron shall be your prophet. You shall speak all that I command you, and your brother Aaron shall tell Pharaoh to let the children of Israel go out of his land. And I will make Pharaoh’s heart hard, and multiply My signs and My wonders (miracles) in the land of Egypt. But Pharaoh will not listen to you, and I shall lay My hand on Egypt and bring out My hosts [like a defensive army, tribe by tribe], My people the children of Israel, out of the land of Egypt by great acts of judgment (the plagues). 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.” And Moses and Aaron did so; just as the LORD commanded them, so they did. Now Moses was eighty years old and Aaron eighty-three years old when they spoke to Pharaoh. Now the LORD said to Moses and Aaron, “When Pharaoh says to you, ‘Work a miracle [to prove your authority],’ then you say to Aaron, ‘Take your staff and throw it down before Pharaoh, so that it may become a serpent.’ ”