Charles Ellicott Commentary Numbers 9:14

"And if a stranger shall sojourn among you, and will keep the passover unto Jehovah; according to the statute of the passover, and according to the ordinance thereof, so shall he do: ye shall have one statute, both for the sojourner, and for him that is born in the land." — Numbers 9:14 (ASV)

And if a stranger ... — The law respecting the stranger is contained in Exodus 12:48-49.