Exodus 12:21-22

21Then 1Moses called for all the elders of Israel and said to them, “2Go and 3take for yourselves 4lambs according to your families, and slay 5the Passover lamb.

226You shall take a bunch of hyssop and dip it in the blood which is in the basin, and 7apply 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.