Exodus 12:21-22

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

22And 5you shall take a bunch of hyssop and dip it in the blood which is in the basin, and 6apply 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.