Exodus 13:15

And when Pharao hardened [his heart so as not] to send us away, he slew every first-born in the land of Egypt, both the first-born of man and the first-born of beast; therefore do I sacrifice every [offspring] that opens the womb, the males to the Lord, and every first-born of my sons I will redeem.

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.

When Pharaoh stubbornly refused to let us go, Yahweh killed all the firstborn in the land of Egypt, both the firstborn of man, and the firstborn of livestock. Therefore I sacrifice to Yahweh all that opens the womb, being males; but all the firstborn of my sons I redeem.’