Exodus 7:9 (KJV)

But Pharaoh shall not hearken unto you, that I may lay my hand upon Egypt, and bring forth mine armies, and my people the children of Israel, out of the land of Egypt by great judgments.

And the Egyptians shall know that I am the LORD, when I stretch forth mine hand upon Egypt, and bring out the children of Israel from among them.

And Moses and Aaron did as the LORD commanded them, so did they.

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,

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.