Exodus 12:19-21

New Revised Standard Version, Anglicised Catholic Edition

¹⁹ For seven days no leaven shall be found in your houses; for whoever eats what is leavened shall be cut off from the congregation of Israel, whether an alien or a native of the land. ²⁰ You shall eat nothing leavened; in all your settlements you shall eat unleavened bread.

²¹ Then Moses called all the elders of Israel and said to them, ‘Go, select lambs for your families, and slaughter the passover lamb.