Exodus 12:23-25

New Revised Standard Version, Anglicised Catholic Edition

²³ For the Lord will pass through to strike down the Egyptians; when he sees the blood on the lintel and on the two doorposts, the Lord will pass over that door and will not allow the destroyer to enter your houses to strike you down. ²⁴ You shall observe this rite as a perpetual ordinance for you and your children. ²⁵ When you come to the land that the Lord will give you, as he has promised, you shall keep this observance.