The Creeds are concise expressions of all that Christians believe. There are three Creeds which are called “ecumenical” because they express that which all Christians should believe and even the Reformed Christians accept these Creeds.
These three Creeds are the Apostles’ Creed, the Nicene Creed and the Athanasian Creed. All three of these date to a time before the Bible was canonized. Below, I’ve printed them out in their entirety, from a Protestant source.
The Apostles’ Creed
I believe in God the Father Almighty, Maker of heaven and earth.
And in Jesus Christ, His only Son, our Lord; who was conceived by the Holy Ghost, born of the Virgin Mary; suffered under Pontius Pilate, was crucified, dead, and buried; He descended into hell; the third day He rose again from the dead; He ascended into heaven, and sitteth on the right hand of God the Father Almighty; from thence He shall come to judge the quick and the dead.
I believe in the Holy Ghost; the holy catholic Church, the communion of saints; the forgiveness of sins; the resurrection of the body; and the life everlasting. Amen.
The Nicene Creed
I believe in one God, the Father Almighty, Maker of heaven and earth, and of all things visible and invisible.
And in one Lord Jesus Christ, the only-begotten Son of God, begotten of the Father before all worlds, God of God, Light of Light, very God of very God, begotten, not made, being of one substance with the Father; by whom all things were made; who for us men, and for our salvation, came down from heaven, and was incarnate by the Holy Ghost of the Virgin Mary, and was made man, and was crucified also for us under Pontius Pilate; He suffered and was buried; and the third day He rose again according to the Scriptures; and ascended into heaven, and sitteth on the right hand of the Father; and He shall come again with glory to judge the quick and the dead; whose kingdom shall have no end.
And I believe in the Holy Ghost, the Lord and Giver of life, who proceedeth from the Father and the Son; who with the Father and the Son together is worshiped and glorified; who spake by the Prophets. And I believe in one holy catholic and apostolic Church.I acknowledge one Baptism for the remission of sins; and I look for the resurrection of the dead, and the life of the world to come. Amen.
The Athanasian Creed
Whosoever will be saved, before all things it is necessary that he hold the catholic faith. Which faith except every one do keep whole and undefiled, without doubt he shall perish everlastingly.
And the catholic faith is this, that we worship one God in Trinity, and Trinity in Unity; Neither confounding the Persons, nor dividing the Substance. For there is one Person of the Father, another of the Son, and another of the Holy Ghost. But the Godhead of the Father, of the Son, and of the Holy Ghost is all one: the glory equal, the majesty coeternal. Such as the Father is, such is the Son, and such is the Holy Ghost. The Father uncreated, the Son uncreated, and the Holy Ghost uncreated. The Father incomprehensible, the Son incomprehensible, and the Holy Ghost incomprehensible. The Father eternal, the Son eternal, and the Holy Ghost eternal. And yet they are not three Eternals, but one Eternal. As there are not three Uncreated nor three Incomprehensibles, but one Uncreated and one Incomprehensible. So likewise the Father is almighty, the Son almighty, and the Holy Ghost almighty. And yet they are not three Almighties, but one Almighty. So the Father is God, the Son is God, and the Holy Ghost is God. And yet they are not three Gods, but one God. So likewise the Father is Lord, the Son Lord, and the Holy Ghost Lord. And yet not three Lords, but one Lord. For like as we are compelled by the Christian verity to acknowledge every Person by Himself to be God and Lord, So are we forbidden by the catholic religion to say, There be three Gods, or three Lords.
The Father is made of none: neither created nor begotten. The Son is of the Father alone; not made, nor created, but begotten. The Holy Ghost is of the Father and of the Son: neither made, nor created, nor begotten, but proceeding. So there is one Father, not three Fathers; one Son, not three Sons; one Holy Ghost, not three Holy Ghosts. And in this Trinity none is before or after other; none is greater or less than another; But the whole three Persons are coeternal together, and coequal: so that in all things, as is aforesaid, the Unity in Trinity and the Trinity in Unity is to be worshiped. He, therefore, that will be saved must thus think of the Trinity.
Furthermore, it is necessary to everlasting salvation that he also believe faithfully the incarnation of our Lord Jesus Christ. For the right faith is, that we believe and confess that our Lord Jesus Christ, the Son of God, is God and Man; God of the Substance of the Father, begotten before the worlds; and Man of the substance of His mother, born in the world; Perfect God and perfect Man, of a reasonable soul and human flesh subsisting. Equal to the Father as touching His Godhead, and inferior to the Father as touching His manhood; Who, although He be God and Man, yet He is not two, but one Christ: One, not by conversion of the Godhead into flesh, but by taking the manhood into God; One altogether; not by confusion of Substance, but by unity of Person. For as the reasonable soul and flesh is one man, so God and Man is one Christ; Who suffered for our salvation; descended into hell, rose again the third day from the dead; He ascended into heaven; He sitteth on the right hand of the Father, God Almighty; from whence He shall come to judge the quick and the dead. At whose coming all men shall rise again with their bodies, and shall give an account of their own works. And they that have done good shall go into life everlasting; and they that have done evil, into everlasting fire.
This is the catholic faith; which except a man believe faithfully and firmly, he cannot be saved.
Did you notice something glaringly absent?
These Creeds contain all the things which a Christian must believe. The first two, the Apostles’ Creed and the Nicene, say, “I believe in the catholic Church”. And the Athanasian says, “it is necessary that he hold the catholic faith”. And then goes on to explain that which is the Catholic faith.
Not one of them says, “I believe that Scripture alone is the sole rule of faith”.
So, none of the Creeds say that we need to believe that Scripture alone is the sole rule of faith. Add to that the fact that Scripture Itself says that the Church is the Pillar of Truth (1 Tim 3:15). And that we should hold Tradition and Scripture (2 Thess 2:15). And you’ve got a devastating argument against Sola Scriptura.