The Federal Republic of Nigeria
Section 2 · 1999 Constitution (2004 edition)
What Constitution says
(1) Nigeria is one indivisible and indissoluble sovereign state to be known by the name of the Federal Republic of Nigeria. (2) Nigeria shall be a Federation consisting of States and a Federal Capital Territory.
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 17. Original document
Release: draft-c8d50d87fae9. Source scope, review and corrections