Exodus 7:8

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.

8 Yahweh spoke to Moses and to Aaron, saying,

9 "When Pharaoh speaks to you, saying, `Perform a miracle!` then you shall tell Aaron, `Take your rod, and cast it down before Pharaoh, that it become a serpent.`"

10 Moses and Aaron went in to Pharaoh, and they did so, as Yahweh had commanded: and Aaron cast down his rod before Pharaoh and before his servants, and it became a serpent.

11 Then Pharaoh also called for the wise men and the sorcerers. They also, the magicians of Egypt, did in like manner with their enchantments.