Exodus 7:5 WEB

³  I will harden Pharaoh's heart, and multiply my signs and my wonders in the land of Egypt.

⁴  But Pharaoh will not listen to you, and I will lay my hand on Egypt, and bring forth my hosts, my people the children of Israel, out of the land of Egypt by great judgments.

⁵  The Egyptians shall know that I am Yahweh, when I stretch forth my hand on Egypt, and bring out the children of Israel from among them.'

⁶  Moses and Aaron did so. As Yahweh commanded them, so they did.

⁷  Moses was eighty years old, and Aaron eighty-three years old, when they spoke to Pharaoh.