Leo the Great, Sermon 77, On Whitsuntide, lii
What the Father has the Son also has, and what the Father and the Son have, the Holy Ghost also has, because the whole Trinity together is One God. But this Faith is not the discovery of earthly wisdom nor the conviction of man�s opinion: the Only-begotten Son has taught it Himself, and the Holy Ghost has established it Himself, concerning Whom no other conception must be formed than is formed concerning the Father and the Son. Because albeit He is not the Father nor the Son, yet He is not separable from the Father and the Son: and as He has His own personality in the Trinity, so has He One substance in Godhead with the Father and the Son, filling all things, containing all things, and with the Father and the Son controlling all things, to Whom is the honor and glory for ever and ever. Amen.