God hardened the Pharaoh's heart
Exodus 4:21 View context
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.
Exodus 9:12 View context
And the LORD hardened the heart of Pharaoh, and he hearkened not unto them; as the LORD had spoken unto Moses.
The Pharaoh harded his own heart
Exodus 8:15 View context
But when Pharaoh saw that there was respite, he hardened his heart, and hearkened not unto them; as the LORD had said.