Citizenship by birth
Section 25(1)(a) · 1999 Constitution (2004 edition)
What Constitution says
(a) every person born in Nigeria before the date of independence, either of whose parents or any of whose grandparents belongs or belonged to a community indigenous to Nigeria; Provided that a person shall not become a citizen of Nigeria by virtue of this section if neither of his parents nor any of his grandparents was born in Nigeria.
This is the 1999 Constitution as published in 2004. Later amendments aren't included yet, so a section may have changed since.
Original source
Official Gazette · CFRN 1999 official PDF · printed page 31. Original document
Release: draft-c8d50d87fae9. Source scope, review and corrections