Permanent incapacity of President or Vice-President
Section 144(1)(a) · 1999 Constitution (2004 edition)
What Constitution says
(a) by a resolution passed by two-thirds majority of all the members of the executive council of the Federation it is declared that the President or Vice-President is incapable of discharging the functions of his office; and
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 72–73. Original document
Release: draft-c8d50d87fae9. Source scope, review and corrections