Exodus 12
22 Ref And take some hyssop and put it in the blood in the basin, touching the two sides and the top of the doorway with the blood from the basin; and let not one of you go out of his house till the morning.
23 Ref For the Lord will go through the land, sending death on the Egyptians; and when he sees the blood on the two sides and the top of the door, the Lord will go over your door and will not let death come in for your destruction.