When Pharaoh stubbornly refused to let us go, the LORD killed the firstborn of both people and animals in Egypt. This is why I sacrifice to the LORD the first male offspring of every womb and redeem each of my firstborn sons.' (NIV)
For when Pharaoh stubbornly refused to let us go, the Lord slew all the firstborn in the land of Egypt, both the firstborn of man and of livestock. Therefore I sacrifice to the Lord all the males that first open the womb; but all the firstborn of my sons I redeem. (AMP)
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. (KJV)