Exodus 12:12-17

For I will go through the land of Egypt on that night, and fatally strike all the firstborn in the land of Egypt, from the human firstborn to animals; and against all the gods of Egypt I will execute judgments—I am the LORD. The blood shall be a sign for you on the houses where you live; and when I see the blood I will pass over you, and no plague will come upon you to destroy you when I strike the land of Egypt. ‘Now this day shall be a memorial to you, and you shall celebrate it as a feast to the LORD; throughout your generations you are to celebrate it as a permanent ordinance. For seven days you shall eat unleavened bread, but on the first day you shall remove dough with yeast from your houses; for whoever eats anything with yeast from the first day until the seventh day, that person shall be cut off from Israel. And on the first day you shall have a holy assembly, and another holy assembly on the seventh day; no work at all shall be done on them, except for what must be eaten by every person—that alone may be prepared by you. You shall also keep the Feast of Unleavened Bread, for on this very day I brought your multitudes out of the land of Egypt; therefore you shall keep this day throughout your generations as a permanent ordinance.