Exodus 12:20

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 shall there be no yeast found in your houses, for whoever eats that which is leavened, that soul shall be cut off from the congregation of Israel, whether he be a foreigner, or one who is born in the land.

Then Moses called for all the elders of Israel, and said to them, "Draw out, and take lambs according to your families, and kill the Passover.

You shall take a bunch of hyssop, and dip it in the blood that is in the basin, and strike the lintel and the two doorposts with the blood that is in the basin; and none of you shall go out of the door of his house until the morning.