Exodus 12:21-23

21Then Moses called for all the elders of Israel, and said to them, Draw out and take for yourselves a lamb according to your families, and kill the passover.1 22And ye shall take a bunch of hyssop, and dip it in the blood that is in the basin, and strike the lintel and the two side posts with the blood that is in the basin; and none of you shall go out at the door of his house till the morning. 23For the LORD will pass through to smite the Egyptians; and when he seeth the blood upon the lintel, and on the two side posts, the LORD will pass over the door, and will not permit the destroyer to come in to your houses to smite you .