Election: two or more presidential candidates
Section 134(4) · 1999 Constitution (2004 edition)
What Constitution says
(4) In default of a candidate duly elected under the foregoing subsections, the Independent National Electoral Commission shall within seven days of the result of the election held under the said subsections, arrange for an election between the two candidates and a candidate at such election shall be deemed elected to the office of President if - (a) he has a majority of votes cast at the election; and (b) he has not less than one-quarter of the votes cast at the election in each of at least two- thirds of all the States in the Federation and the Federal Capital Territory, Abuja
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 68. Original document
Release: draft-c8d50d87fae9. Source scope, review and corrections