Exodus 12:24 in the King James Version
And ye shall observe this thing for an ordinance to thee and to thy sons for ever.
Context
23 For the LORD will pass through to strike the Egyptians; and when he sees the blood on the lintel, and on the two door posts, the LORD will pass over the door, and will not allow the destroyer to come in to your houses to strike you.
24 You shall observe this thing for an ordinance to you and to your sons forever.
25 It shall happen when you have come to the land which the LORD will give you, as he has promised, that you shall keep this service.