Exodus 7:5-9

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.

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

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

And the LORD spake unto Moses and unto Aaron, saying,

When Pharaoh shall speak unto you, saying, Shew a miracle for you: then thou shalt say unto Aaron, Take thy rod, and cast it before Pharaoh, and it shall become a serpent.