Exodus 12:18-20
18 In 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.
19 For seven days no yeast is to be found in your houses. And whoever eats anything with yeast in it must be cut off from the community of Israel, whether he is an alien or native-born.
20 Eat nothing made with yeast. Wherever you live, you must eat unleavened bread.”