Concerning which subject, leaving the judgment to the decision of the reader, I warn him Daniel is not to be found in the Prophets among the Hebrews, but among those which they titled the Hagiographa. Since indeed all of Scripture is divided by them into three parts, into the Law, into the Prophets, (and) into the Hagiographa, that is, into five and eight and eleven books, which is not (necessary) to explain at this time. And to those things of this prophet, or rather against this book, which Porphyry accused, the witnesses are Methodius, Eusebius, (and) Apollinaris, who, responding to his madness with many thousands of verses, I do not know whether they are satisfying to the interested reader. For which reason I entreat you, O Paula and Eustochium, pour out prayers for me to the Lord, so that as long as I am in this little body, I might write something pleasing to you, useful to the Church, (and) worthy to posterity. I am indeed not greatly moved by the judgments of the present, which on either side are in error either by love or by hate.
You can find the complete Prologue here: http://www.tertullian.org/fathers/jerome_preface_daniel.htm