Strong H7185 קָשָׁה qâshâh · to harden

Exodus

1. Exodus 7:3
   And I will harden Pharaoh’s heart, and multiply my signs and my wonders in the land of Egypt.
2. Exodus 13:15
   And it came to pass, when Pharaoh would hardly let us go, that the Lord slew all the firstborn in the land of Egypt, both the firstborn of man, and the firstborn of beast: therefore I sacrifice to the Lord all that openeth the matrix, being males; but all the firstborn of my children I redeem.