Appointment of Chief Justice of Nigeria and Justices of the Supreme Court
Section 231(3) · 1999 Constitution (2004 edition)
What Constitution says
(3) A person shall not be qualified to hold the office of Chief Justice of Nigeria or a Justice of the Supreme Court, unless he is qualified to practice as a legal practitioner in Nigeria and has been so qualified for a period of not less than fifteen years.
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 101. Original document
Release: draft-c8d50d87fae9. Source scope, review and corrections