Exodus 7:3; Exodus 13:15

Exodus 7:3

3 "But I will harden Pharaoh's heart that I may multiply My signs and My wonders in the land of Egypt.

Exodus 13:15

15 'It came about, when Pharaoh was stubborn about letting us go, that the LORD killed every firstborn in the land of Egypt, both the firstborn of man and the firstborn of beast. Therefore , I sacrifice to the LORD the males, the first offspring of every womb, but every firstborn of my sons I redeem.'