Exodus 12:18-20

18You are to eat unleavened bread in the first month, from the evening of the fourteenth day of the month until the evening of the twenty-first day.

19Yeast must not be found in your houses for seven days. If anyone eats something leavened, that person, whether a resident alien or native of the land, must be cut off from the community of Israel.

20Do not eat anything leavened; eat unleavened bread in all your homes.”