Exodus 7:5

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

⁴  But Pharaoh shall not hearken unto you, that I may lay my hand upon Egypt, and bring forth mine 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 forth mine hand upon Egypt, and bring out the children of Israel from among them.

⁶  And Moses and Aaron did as the LORD commanded them, so did they.

⁷  And Moses was fourscore years old, and Aaron fourscore and three years old, when they spake unto Pharaoh.