Exodus 12:18-20

18In the first month, from the fourteenth day of the month at evening, you shall eat unleavened bread until the twenty-first day of the month at evening. 19For seven days no leaven is to be found in your houses. If anyone eats what is leavened, that person will be cut off from the congregation of Israel, whether he is a sojourner or a native of the land. 20You shall eat nothing leavened; in all your dwelling places you shall eat unleavened bread.”