Exodus 12:18-20

18In the first month you are to eat unleavened bread, from the evening of the fourteenth day until the evening of the twenty-first day. 19For seven days there must be no leaven found in your houses. If anyone eats something leavened, that person, whether a foreigner or native of the land, must be cut off from the congregation of Israel. 20You are not to eat anything leavened; eat unleavened bread in all your homes.”