Exodus 12:23-28

For the LORD will pass through to strike the Egyptians, and when he sees the blood on the lintel and on the two doorposts, the LORD will pass over the door and will not allow the destroyer to enter your houses to strike you. You shall observe this rite as a statute for you and for your sons forever. And when you come to the land that the LORD will give you, as he has promised, you shall keep this service. And when your children say to you, ‘What do you mean by this service?’ you shall say, ‘It is the sacrifice of the LORD’s Passover, for he passed over the houses of the people of Israel in Egypt, when he struck the Egyptians but spared our houses.’” And the people bowed their heads and worshiped. Then the people of Israel went and did so; as the LORD had commanded Moses and Aaron, so they did.