Nicene and Post-Nicene Fathers, Ser. II, Vol. III:
Life and Works of Rufinus with Jerome's Apology Against Rufinus.: Jerome's attack upon Ambrose.

23. You see by this what his opinions are about Origen and also about Ambrose. If he should deny that his strictures apply to Ambrose, which every one knows, he will be convicted in the first place by the fact that there is a Commentary of his on Luke which is current among the Latins, and none by any other hand. But secondly he knows that I possess a letter of his in which, while he discharges others, he makes his strictures fall upon Ambrose. But, since that letter contains certain more secret matters, I do not wish to see it published before the right time; and therefore I will corroborate what I say by other proofs similar to it. In the meantime let this be counted as demonstrated by what I have said above, that he extols Origen’s writings as in every way admirable, and declares that ‘if he translates them, the Roman tongue will then recognize what a store of good it had hitherto been ignorant of and now has begun to understand,’ that is the twenty six books on Matthew, the five on Luke, and the thirty two on John. These are the books to which he gives the highest honour; and in these absolutely everything is to be found which is contained in the books on Περὶ ᾽Αρχῶν, the groundwork of his charges against me, only set forth with greater breadth and fulness. If then he promises that he will translate these, why does he condemn me for a similar course? But now I have undertaken to prove how violently he attacks a man who is worthy of all admiration, Ambrose, Bishop of Milan, who was not to that church alone but to all the churches like a column or an impregnable fortress. I will therefore set forth a Preface of his by which you may see in what foul and unworthy terms he assails even a man of such eminence, and also how he praises Didymus to the sky, though he has since cast him down even to the infernal region; and further how he speaks of the city of Rome, which now through the grace of God is reckoned by Christians as their capital, words which were only applicable when its inhabitants were a nation who were heathens and princes who were persecutors.