Exodus 12:12-15

“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.