Exodus 7:8-13

8And the LORD spoke to Moses and to Aaron, saying, 9When Pharaoh shall speak to you, saying, Show a miracle for you: then thou shalt say to Aaron, Take thy rod, and cast it before Pharaoh, and it shall become a serpent. 10And Moses and Aaron went in to Pharaoh, and they did so as the LORD had commanded: and Aaron cast down his rod before Pharaoh, and before his servants, and it became a serpent. 11Then Pharaoh also called the wise men and the sorcerers: now the magicians of Egypt, they also did in like manner with their enchantments. 12For they cast down every man his rod, and they became serpents: but Aaron’s rod swallowed up their rods. 13And he hardened Pharaoh’s heart, that he hearkened not to them; as the LORD had said.