33 Now these the divinely-inspired Scriptures of both the Old and the New Testament teach us. For the God of the two Testaments is One, Who in the Old Testament foretold the Christ Who appeared in the New; Who by the Law and the Prophets led us to Christ's school. For before faith came, we were kept in ward under the law, and, the law has been our tutor to bring us unto Christ. And if ever thou hear any of the heretics speaking evil of the Law or the Prophets, answer in the sound of the Saviour's voice, saying, Jesus came not to destroy the Law, but to fulfil it. Learn also diligently, and from the Church, what are the books of the Old Testament, and what those of the New. And, pray, read none of the apocryphal writings: for why do you, who know not those which are acknowledged among all, trouble yourself in vain about those which are disputed? Read the Divine Scriptures, the twenty-two books of the Old Testament, these that have been translated by the Seventy-two Interpreters.
Source: Catechetical Lectures (New Advent)