Exod 12:27 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 He said,“Certainly I will be with you, and this shall be a sign to you that it is I who have sent you: when you have brought the people out of Egypt,
you shall worship God at this mountain” Exod.