Exodus 7:8-14

And Jehovah spake unto Moses and unto Aaron, saying, When Pharaoh shall speak unto you, saying, Show a wonder for you; then thou shalt say unto Aaron, Take thy rod, and cast it down before Pharaoh, that it become a serpent. And Moses and Aaron went in unto Pharaoh, and they did so, as Jehovah had commanded: and Aaron cast down his rod before Pharaoh and before his servants, and it became a serpent. Then Pharaoh also called for the wise men and the sorcerers: and they also, the magicians of Egypt, did in like manner with their enchantments. For they cast down every man his rod, and they became serpents: but Aaron’s rod swallowed up their rods. And Pharaoh’s heart was hardened, and he hearkened not unto them; as Jehovah had spoken. And Jehovah said unto Moses, Pharaoh’s heart is stubborn, he refuseth to let the people go.