Restrictions on formation of political parties
Section 222(b) · 1999 Constitution (2004 edition)
What Constitution says
(b) the membership of the association is open to every citizen of Nigeria irrespective of his place of origin, circumstance of birth, sex, religion or ethnic grouping;
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 98. Original document
Release: draft-c8d50d87fae9. Source scope, review and corrections