There is, brethren, one God, the knowledge of whom we gain from the Holy Scriptures, and from no other source. For just as a man if he wishes to be skilled in the wisdom of this world, will find himself unable to get at it in any other way than by mastering the dogmas of philosophers, so all of us who wish to practise piety will be unable to learn its practice from any other quarter than the oracles of God. Whatever things then the Holy Scriptures declare, at these let us look; and whatsoever things they teach these let us learn." (Against the Heresy of One Noetus, 9)
Athanasius wrote:
"Vainly then do they run about with the pretext that they have demanded Councils for the faith's sake; for divine Scripture is sufficient above all things; but if a Council be needed on the point, there are the proceedings of the Fathers, for the Nicene Bishops did not neglect this matter, but stated the doctrines so exactly, that persons reading their words honestly, cannot but be reminded by them of the religion towards Christ announced in divine Scripture" (De Synodis, 6)
Cyril of Jerusalem wrote:
"For concerning the divine and sacred Mysteries of the Faith, we ought not to deliver even the most casual remark without the Holy Scriptures: nor be drawn aside by mere probabilities and the artifices of argument. Do not then believe me because I tell thee these things, unless thou receive from the Holy Scriptures the proof of what is set forth: for this salvation, which is of our faith, is not by ingenious reasonings, but by proof from the Holy Scriptures." (Lecture 4:17)
Even if nobody had advocated sola scriptura before the Reformation, the truth would remain the truth. The scriptures are the only apostolic material we have today. As such, they're the voice of the apostles, and they speak louder than all other traditions.
Early Christians on Tradition and we are to follow the Catholic Church teaching
“But what is also to the point, let us note that the very TRADITION, teaching and faith of the CATHOLIC CHURCH from the beginning, WHICH THE LORD GAVE, was preached by the Apostles, and was preserved by the Fathers. On this was the Church founded; and if anyone departs from this, he neither is nor any longer ought to be called a Christian.”
St. Athanasius, Letters to Serapion of Thmuis, 1,28, 359 A.D
Saint Irenaeus
“Those, therefore, who desert the PREACHING OF THE CHURCH, call in question the knowledge of the holy presbyters, not taking into consideration of how much greater consequence is a religious man, even in a private station, than a blasphemous and impudent sophist. Now, such are all the heretics, and those who imagine that they have hit upon something more beyond the truth, so that by following those things already mentioned, proceeding on their way variously, in harmoniously, and foolishly, not keeping always to the same opinions with regard to the same things, as blind men are led by the blind, they shall deservedly fall into the ditch of ignorance lying in their path, ever seeking and never finding out the truth. It behooves us, therefore, to avoid their doctrines, and to take careful heed lest we suffer any injury from them; but to FLEE TO THE CHURCH, and be brought up in her bosom, and be nourished with the Lord’s Scriptures.” Irenaeus, Against Heresies, 5,20:2 (A.D. 180)
Saint Gregory of Nyssa
“[S]eeing, I say, that the CHURCH teaches this in plain language, that the Only-begotten is essentially God, very God of the essence of the very God, how ought one who opposes her decisions to overthrow the preconceived opinion... And let no one interrupt me, by saying that what we confess should also be confirmed by constructive reasoning: for it is enough for proof of our statement, that the TRADITION has come down to us from our Fathers, handled on, like some inheritance, by succession from the apostles and the saints who came after them.” Gregory of Nyssa, Against Eunomius, 4:6 (c. A.D. 384).
Saint Ambrose
“Wherefore all other generations are strangers to truth; all the generations of heretics hold not the truth: the CHURCH ALONE, with pious affection, is in possession of the truth.” Ambrose, Commentary of Psalm 118,19 (A.D. 388).
Saint Augustine
“Let us not hear, this I say, this you say; but thus says the Lord. Surely it is the books of the Lord on whose authority we both agree and which we both believe. There let us seek the Church, there let us discuss our case.” He goes on: “Neither dare one agree with catholic bishops if by chance they err in anything, with the result that their opinion is against the canonical Scriptures of God.” -
Augustine (”De unitate ecclesiae”, [on the Unity of the Church]3)
“But in regard to those observances which we carefully attend and which the whole world keeps, and which derive not from Scripture BUT FROM TRADITION, we are given to understand that they are recommended and ordained to be kept either by the Apostles themselves or by plenary COUNCILS, THE AUTHORITY OF WHICH IS QUITE VITAL TO THE CHURCH.”-Letter of Augustine to Januarius 54,1,1, 400 A.D.
Saint Jerome
“My resolution is, to read the ancients, to try everything, to hold fast what is good, and not to recede from the faith of the CATHOLIC CHURCH.” Jerome, To Minervius & Alexander, Epistle 119 (A.D. 406).
Saint Basil
“Now I accept no newer creed written for me by other men, nor do I venture to propound the outcome of MY OWN intelligence, lest I make the words of true religion merely human words; but what I have been taught by the holy Fathers, that I announce to all who question me. In my CHURCH the creed written by the holy Fathers in synod at Nicea is in use.” Basil, To the Church of Antioch, Epistle 140:2 (A.D. 373).