Exodus 13:15 yea, it cometh to pass, when Pharaoh hath been pained to send us away, that Jehovah doth slay every first-born in the land of Egypt, from the first-born of man even unto the first-born of beast; therefore I am sacrificing to Jehovah all opening a womb who `are' males, and every first-born of my sons I ransom; (Young's Literal Translation)