Presidential appointments
Section 171(3) · 1999 Constitution (2004 edition)
What Constitution says
(3) An appointment to the office of the Head of the Civil Service of the Federation shall not be made except from among Permanent Secretaries or equivalent rank in the civil service of the Federation or of a State.
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 81. Original document
Release: draft-c8d50d87fae9. Source scope, review and corrections