Exodus 12:6, 18-20

Now you shall keep it until the fourteenth day of the same month. Then the whole assembly of the congregation of Israel shall kill it at twilight.

In 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. For seven days no leaven shall be found in your houses, since whoever eats what is leavened, that same person shall be cut off from the congregation of Israel, whether he is a stranger or a native of the land. You shall eat nothing leavened; in all your dwellings you shall eat unleavened bread.’ ”