The Catholic Encyclopedia: An International Work of Reference on the Constitution, Doctrine, Discipline and History of the Catholic Church Volume 12 page 44 Charles G. Herbermann, Edward A. Pace, Conde B. Pallen, Thomas J. Shahan, John J. Wynne Publisher: Encyclopedia Press, Inc. (1915) ASIN: B0013UCA4K [3]
"Photius and the later Eastern controversialists dropped or rejected the per Filium, as being nearly equivalent to ex Filio or Filioque, or understood it as being applicable only to the mission of the Spirit, and emphasized the exclusiveness of the procession from the Father" (Philip Schaff, History of the Christian Church, volume IV, §108).
"Leo III". The lives of the eighth-century popes (Liber pontificalis) : the ancient biographies of nine popes from AD 715 to AD 817. Raymond Davis (2nd rev. ed.). Liverpool: Liverpool University Press. 2007. p. 216. ISBN978-1-84631-154-3. OCLC222145811.{{cite book}}: CS1 maint: others (link)
