Exodus 12:18-20

181In the first month, on the fourteenth day of the month at evening, you shall eat unleavened bread, until the twenty-first day of the month at evening. 19For 2seven days there shall be no dough with yeast found in your houses; for whoever eats anything with yeast, that 34person shall be cut off from the congregation of Israel, whether he is a stranger or a native of the land. 20You shall not eat anything with yeast; in all your dwellings you shall eat unleavened bread.’”