Sola Scriptura properly understood is not “if it is not in the Bible I will not believe it” but rather Scripture above tradition.
Luther determined to follow the practice of Augustine in these matters, who in a letter to Jerome wrote, “I have learned to do only those books that are called the Holy Scriptures the honor of believing firmly that none of their writes has ever erred. All others I so read as not to hold what they say to be truth unless they prove it to me by Holy Scripture or clear reason.”
quodlibet.net/luther.shtml
It depends again on the Protestant for how they view Scripture and Tradition. There are indeed many who reject any doctrine from Tradition if it’s not
explicit in the Bible. (although all Protestants I’ve met hold to doctrines not explicit in Scripture)
Just for reference, Augustine did not practice Sola Scriptura by that statement, or others of his:*I desire you therefore, in the first place, to hold fast this as the fundamental principle in the present discussion, that our Lord Jesus Christ has appointed to us a light yoke and an easy burden, as He declares in the Gospel: Matthew 11:30 in accordance with which He has bound His people under the new dispensation together in fellowship by sacraments, which are in number very few, in observance most easy, and in significance most excellent, as baptism solemnized in the name of the Trinity, the communion of His body and blood, and such other things as are prescribed in the canonical Scriptures, with the exception of those enactments which were a yoke of bondage to God’s ancient people, suited to their state of heart and to the times of the prophets, and which are found in the five books of Moses. As to those other things which
we hold on the authority, not of Scripture, but of tradition, and which are observed throughout the whole world, it may be understood that they are held as approved and instituted either by the apostles themselves, or by plenary Councils, whose authority in the Church is most useful, e.g. the annual commemoration, by special solemnities, of the Lord’s passion, resurrection, and ascension, and of the descent of the Holy Spirit from heaven, and whatever else is in like manner observed by the whole Church wherever it has been established. (
Letter to Januarius 54.1)
For this question of baptism had not been as yet completely worked out, but yet the Church observed the most wholesome custom of correcting what was wrong, not repeating what was already given, even in the case of schismatics and heretics: she healed the wounded part, but did not meddle with what was whole. And this custom, coming, I suppose, from
apostolical tradition (like many other things which are held to have been handed down under their actual sanction, because they are preserved throughout the whole Church, though they are not found either in their letters, or in the Councils of their successors),— this most wholesome custom, I say, according to the holy Cyprian, began to be what is called amended by his predecessor Agrippinus. (
On Baptism, 2.7.12)*