Exodus 12:21-28

Then Moses called for all the elders of Israel, and said unto them, Draw out and take you a lamb according to your families, and kill the passover. And ye shall take a bunch of hyssop, and dip it in the blood that is in the bason, and strike the lintel and the two side posts with the blood that is in the bason; and none of you shall go out at the door of his house until the morning. For 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 suffer the destroyer to come in unto your houses to smite you. And ye shall observe this thing for an ordinance to thee and to thy sons for ever. And it shall come to pass, when ye be come to the land which the LORD will give you, according as he hath promised, that ye shall keep this service. And it shall come to pass, when your children shall say unto you, What mean ye by this service? That ye shall say, It is the sacrifice of the LORD's passover, who passed over the houses of the children of Israel in Egypt, when he smote the Egyptians, and delivered our houses. And the people bowed the head and worshipped. And the children of Israel went away, and did as the LORD had commanded Moses and Aaron, so did they.