8 Augustine replied: We give to the whole Old Testament Scriptures their due praise as true and divine; you impugn the Scriptures of the New Testament as having been tampered with and corrupted. Those things in the Old Testament which we do not observe we hold to have been suitable appointments for the time and the people of that dispensation, besides being symbolic to us of truths in which they have still a spiritual use, though the outward observance is abolished; and this opinion is proved to be the doctrine of the apostolic writings. You, on the other hand, find fault with everything in the New Testament which you do not receive, and assert that these passages were not spoken or written by Christ or His apostles. In these respects there is a manifest difference between us. When, therefore, you are asked why you do not receive all the contents of the New Testament, but, while you approve of some things, reject a great many in the very same books as false and spurious interpolations, you must not pretend to imitate us in the distinction which we make, reverently and in faith, but must give account of your own presumption.
Source: Reply to Faustus the Manichaean (New Advent)