Exodus 13:15

Exodus 13:15 AMP

For it happened, when Pharaoh stubbornly refused to let us go, that the LORD struck every firstborn in the land of Egypt, both the firstborn of man and the firstborn of animal. Therefore, I sacrifice to the LORD all the males, the first [to be born] of every womb, but every firstborn of my sons I redeem.’
AMP: Amplified Bible