Exodus 12:15

For I will go through the land of Egypt in that night, and will strike all the firstborn in the land of Egypt, both man and animal. I will execute judgments against all the gods of Egypt. I am the LORD.

The blood shall be to you for a token on the houses where you are. When I see the blood, I will pass over you, and no plague will be on you to destroy you when I strike the land of Egypt.

This day shall be a memorial for you. You shall keep it as a feast to the LORD. You shall keep it as a feast throughout your generations by an ordinance forever.

In the first day there shall be to you a holy convocation, and in the seventh day a holy convocation; no kind of work shall be done in them, except that which every man must eat, only that may be done by you.

You shall observe the feast of unleavened bread; for in this same day I have brought your armies out of the land of Egypt. Therefore you shall observe this day throughout your generations by an ordinance forever.

In the first month, on the fourteenth day of the month at evening, you shall eat unleavened bread, until the twenty first day of the month at evening.