Exodus 12:23-28

When the LORD goes through the land to strike down the Egyptians, he will see the blood on the top and sides of the door-frame and will pass over that doorway, and he will not permit the destroyer to enter your houses and strike you down. ‘Obey these instructions as a lasting ordinance for you and your descendants. When you enter the land that the LORD will give you as he promised, observe this ceremony. And when your children ask you, “What does this ceremony mean to you?” then tell them, “It is the Passover sacrifice to the LORD, who passed over the houses of the Israelites in Egypt and spared our homes when he struck down the Egyptians.” ’ Then the people bowed down and worshipped. The Israelites did just what the LORD commanded Moses and Aaron.