Exodus 12:17-22

You shall also observe the Feast of Unleavened Bread, for on this very day I brought your hosts out of the land of Egypt; therefore you shall observe this day throughout your generations as a permanent ordinance. 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. Seven days there shall be no leaven found in your houses; for whoever eats what is leavened, that person shall be cut off from the congregation of Israel, whether he is an alien or a native of the land. You shall not eat anything leavened; in all your dwellings you shall eat unleavened bread.’ ” Then Moses called for all the elders of Israel and said to them, “Go and take for yourselves lambs according to your families, and slay the Passover lamb. You shall take a bunch of hyssop and dip it in the blood which is in the basin, and apply some of the blood that is in the basin to the lintel and the two doorposts; and none of you shall go outside the door of his house until morning.