12 And the LORD hardened the heart of Pharaoh, and he hearkened not unto them; as the LORD had spoken unto Moses.
Exodus 9:12 Cross References - KJV
Exodus 4:21
21 And the LORD said unto Moses, When thou goest to return into Egypt, see that thou do all those wonders before Pharaoh, which I have put in thine hand: but I will harden his heart, that he shall not let the people go.