Exodus 12:12-28 NIV
“On that same night I will pass through Egypt and strike down every firstborn of both people and animals, and I will bring judgment on all the gods of Egypt. I am the LORD. The blood will be a sign for you on the houses where you are, and when I see the blood, I will pass over you. No destructive plague will touch you when I strike Egypt.
“This is a day you are to commemorate; for the generations to come you shall celebrate it as a festival to the LORD—a lasting ordinance. For seven days you are to eat bread made without yeast. On the first day remove the yeast from your houses, for whoever eats anything with yeast in it from the first day through the seventh must be cut off from Israel. On the first day hold a sacred assembly, and another one on the seventh day. Do no work at all on these days, except to prepare food for everyone to eat; that is all you may do.
“Celebrate the Festival of Unleavened Bread, because it was on this very day that I brought your divisions out of Egypt. Celebrate this day as a lasting ordinance for the generations to come. In the first month you are to eat bread made without yeast, from the evening of the fourteenth day until the evening of the twenty-first day. For seven days no yeast is to be found in your houses. And anyone, whether foreigner or native-born, who eats anything with yeast in it must be cut off from the community of Israel. Eat nothing made with yeast. Wherever you live, you must eat unleavened bread.”
Then Moses summoned all the elders of Israel and said to them, “Go at once and select the animals for your families and slaughter the Passover lamb. Take a bunch of hyssop, dip it into the blood in the basin and put some of the blood on the top and on both sides of the doorframe. None of you shall go out of the door of your house until morning. When the LORD goes through the land to strike down the Egyptians, he will see the blood on the top and sides of the doorframe 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 worshiped. The Israelites did just what the LORD commanded Moses and Aaron.
NIV: New International Version