Exodus 12:22-24

22And 1you shall take a bunch of hyssop and dip it in the blood which is in the basin, and 2apply 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.

23For 3the Lord will pass through to strike the Egyptians; but when He sees the blood on the lintel and on the two doorposts, the Lord will pass over the door and will 4not allow the 5destroyer to come in to your houses to strike you.

24And 6you shall keep this event as an ordinance for you and your children forever.