St. Vincent of Lerins | The "Vincentian Canon", AD 434
Now in the Catholic Church itself we take the greatest care to hold that which has been believed everywhere, always and by all. That is truly and properly 'Catholic,' as is shown by the very force and meaning of the word, which comprehends everything almost universally.
Ignatius of Antioch | Letter to the Smyrnaeans 8:2 [A.D 110]
Let no one do anything of concern to the Church without the bishop. Let that be considered a valid Eucharist which is celebrated by the bishop or by one whom he ordains. Wherever the bishop appears, let the people be there; just as wherever Jesus Christ is, there is the Catholic Church.
Cyril of Jerusalem | Catechetical Lectures 18:23 [A.D 350]
The Church is called Catholic, then, because it extends over the whole world, from end to end of the earth, and because it teaches universally and infallibly each and every doctrine which must come to the knowledge of men...
St. Augustine | Against the Letter of Mani Called "The Foundation" 4:5 [A.D. 297]
Indeed, I would not believe in the gospel myself if the authority of the Catholic Church did not move me to do so.