Exodus 13:15

JPS_ASV_Byz(i) 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 first-born of man, and the first-born of beast; therefore I sacrifice to the LORD all that openeth the womb, being males; but all the first-born of my sons I redeem.