Exodus 7:13 KJV

And he hardened Pharaoh’s heart, that he hearkened not unto them; as the Lord had said.
Exodus 7:13, King James Version

In context

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.