Exodus 12:17-20

17“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.

18In 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.

19For 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.

20Eat nothing made with yeast. Wherever you live, you must eat unleavened bread.”