Exodus 12:17-20

17So you will keep the Feast of Unleavened Bread, because on this very day I brought your regiments out from the land of Egypt, and so you must keep this day perpetually as a lasting ordinance.

18In the first month, from the fourteenth day of the month, in the evening, you will eat bread made without yeast until the twenty-first day of the month in the evening.

19For seven days yeast must not be found in your houses, for whoever eats what is made with yeast – that person will be cut off from the community of Israel, whether a foreigner or one born in the land.

20You will not eat anything made with yeast; in all the places where you live you must eat bread made without yeast.’”