Exodus 12:6, 18-20

You shall keep it until the fourteenth day of the same month, then the whole assembly of the congregation of Israel is to slaughter it at twilight.

In the first month, on the fourteenth day of the month at evening, you shall eat unleavened bread, [and continue] until the twenty-first day of the month at evening. Seven days no leaven shall be found in your houses; whoever eats what is leavened shall be cut off and excluded from [the atonement made for] the congregation of Israel, whether a stranger or native-born. [1 Cor 5:6-8] You shall eat nothing leavened; in all your dwellings you shall eat unleavened bread.’ ”