New states and boundary adjustment, etc
Section 8(1) · 1999 Constitution (2004 edition)
What Constitution says
(1) An Act of the National Assembly for the purpose of creating a new State shall only be passed if- (a) a request, supported by at least two-thirds majority of members (representing the area demanding the creation of the new State) in each of the following, namely - (i) the Senate and the House of Representatives, (ii) the House of Assembly in respect of the area, and (iii) the local government councils in respect of the area, is received by the National Assembly; (b) a proposal for the creation of the State is thereafter approved in a referendum by at least two-thirds majority of the people of the area where the demand for creation of the State originated; (c) the result of the referendum is then approved by a simple majority of all the States of the Federation supported by a simple majority of members of the Houses of Assembly; and (d) the proposal is approved by a resolution passed by two-thirds majority of members of each House of the National Assembly.
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 22–24. Original document
Release: draft-c8d50d87fae9. Source scope, review and corrections