Exodus 12:22-26

And you shall take a bunch of hyssop and dip it in the blood which is in the basin, and apply 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. A Memorial of Redemption

For the 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 not allow the destroyer to come in to your houses to strike you.

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

When you enter the land which the Lord will give you, as He has promised, you shall keep this rite.

And when your children say to you, ‘What does this rite mean to you?’