Pope Boniface VIII, Bull Unam sanctam (1302): "We are compelled in virtue of our faith to believe and maintain that there is only one holy Catholic Church, and that one is apostolic. This we firmly believe and profess without qualification. Outside this Church there is no salvation and no remission of sins, the Spouse in the Canticle proclaiming: 'One is my dove, my perfect one. One is she of her mother, the chosen of her that bore her' (Canticle of Canticles 6:8); which represents the one mystical body whose head is Christ, of Christ indeed, as God. And in this, 'one Lord, one faith, one baptism' (Ephesians 4:5). Certainly Noah had one ark at the time of the flood, prefiguring one Church which perfect to one cubit having one ruler and guide, namely Noah, outside of which we read all living things were destroyed… We declare, say, define, and pronounce that it is absolutely necessary for the salvation of every human creature to be subject to the Roman Pontiff."Pope Boniface VIII, Unam Sanctam: (Promulgated November 18, 1302) “We declare, say, define, and pronounce [ex cathedra] that it is absolutely necessary for the salvation of every human creature to be subject to the Roman Pontiff.”
"If, therefore, the Greeks or others say that they are not committed to Peter and to his successors, they necessarily say that they are not of the sheep of Christ, since the Lord says that there is only one fold and one shepherd (Jn.10:16). Whoever, therefore, resists this authority, resists the command of God Himself. " — Pope Boniface VIII, Unam Sanctam (Promulgated November 18, 1302)
http://www.fordham.edu/halsall/source/b8-unam.html