And you shall observe this thing as an ordinance for you and your sons forever.
Exodus 12:24
Surrounding context
12:23 For the LORD will pass through to strike the Egyptians; and when He sees the blood on the lintel and on the two doorposts, the LORD will pass over the door and not allow the destroyer to come into your houses to strike you.
12:24 And you shall observe this thing as an ordinance for you and your sons forever.
12:25 It will come to pass when you come to the land which the LORD will give you, just as He promised, that you shall keep this service.