Exodus 13:15

When Pharaoh stubbornly refused to let us go, the LORD killed every firstborn in Egypt, both man and animal. This is why I sacrifice to the LORD the first male offspring of every womb and redeem each of my firstborn sons.'

(New International Version)

'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.'

(New American Standard Bible)

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.

(King James Version)