Exodus 12:13-15

13The blood will be a sign for you on the houses where you are, so that when I see the blood I will pass over you, and this plague will not fall on you to destroy you when I attack the land of Egypt.

14This day will become a memorial for you, and you will celebrate it as a festival to the Lord – you will celebrate it perpetually as a lasting ordinance.

15For seven days you must eat bread made without yeast. Surely on the first day you must put away yeast from your houses because anyone who eats bread made with yeast from the first day to the seventh day will be cut off from Israel.