Sola Scriptura -- It's Not Taught in the Bible
For Catholics, Holy Scripture certainly is a “standard of truth”, but not in a sense that rules out the authority of authentic apostolic tradition and the Church.
Catholics agree with Protestants that Scripture is materially sufficient: i.e., every true doctrine can be found in the Bible, if only implicitly and indirectly by deduction. But no biblical passage teaches that Scripture is the sole rule of faith for the Christian (formal sufficiency). Nor can Sola Scriptura be deduced from implicit passages!
The Catholic Church teaches that Christ entrusted the preaching of the Gospel to the apostles, who handed it on orally and in writing, and according to the Catechism of the Catholic Church, "the apostolic preaching, which is expressed in a special way in the inspired books, was to be preserved in a continuous line of succession until the end of time. This living transmission, accomplished in the Holy Spirit, is called Tradition, since it is distinct from Sacred Scripture, though closely connected to it." "Sacred Tradition and Sacred Scripture make up a single sacred deposit of the Word of God in which, as in a mirror, the pilgrim Church contemplates God, the source of all her riches." For the Eastern Orthodox too, "the Holy Bible forms a part of Holy Tradition but does not lie outside of it. One would be in error to suppose that Scripture and Tradition are two separate and distinct sources of Christian Faith, as some do, since there is, in reality, only one source; and the Holy Bible exists and found its formulation within Tradition"