Exodus 7:11

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

9 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.

10 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.

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

12 For they cast down every man his rod, and they became serpents: but Aaron's rod swallowed up their rods.

13 And he hardened Pharaoh's heart, that he hearkened not unto them; as the LORD had said.

14 And the LORD said unto Moses, Pharaoh's heart is hardened, he refuseth to let the people go.