Exodus 7:7-14

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. And Moses and Aaron went in unto 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. Then Pharaoh also called the wise men and the sorcerers: now the magicians of Egypt, they also 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 he hardened Pharaoh's heart, that he hearkened not unto them; as the LORD had said. And the LORD said unto Moses, Pharaoh's heart is hardened, he refuseth to let the people go.