Augustine wrote hundreds of letters to priests and bishops in the Church. Many of the letters are written in response to questions that he had received from them, some of which Augustine did not necessarily think were worth his time and effort, but were a burden to address, and provide responses to:
~I have not at my disposal sufficient leisure to enter on the refutation of his opinions one by one: my time is demanded by other
and more important work. (Augustine to Casulanus, A.D.396)
~You have sent suddenly upon me a countless multitude of questions, by which you must have purposed to blockade me on every side, or
rather bury me completely, even if you were under the impression that
I was otherwise unoccupied and at leisure; for how could I, even
though wholly at leisure, furnish the solution of so many questions to
one in such haste as you are, and, in fact, as you write, on the eve
of a journey? ... You seem to me to be prompted to mental effort night and day by no other motive than ambition to be praised by men for your industry and
acquisitions in learning. (Augustine to Dioscorus, A.D.410)
In the same letter to Casulanus quoted above, in which Casulanus asks if it is lawful to fast on the seventh day of the week (a thing forbidden by the tradition of the elders), the translators left out 6 chapters of the letter, giving this explanation:
"We have no compunction in passing over about eight columns here of
this letter, in which Augustine exposes, with a tedious minuteness and
with a waste of rhetoric, other feeble and irrelevant puerilities of
the Roman author whose work Casulanus had submitted to his review.
Instead of accompanying him into the shallow places into which he was
drawn while pursuing such an insignificant foe, let us resume the
translation at the point at which Augustine gives his own opinion
regarding the question whether it is binding on Christians to fast on
It's apparent in this example that Augustine didn't appreciate the Church being troubled by questions about old traditions, I imagine that there are many more and much better examples that can be gleaned from these letters.
-> A comprehensive listing of Augustines works that have been translated into english.
I've been sifting through his letters trying to find one where Augustine compares certain bishops to the letter-of-the-law Pharisees or Sadducees, but the amount of reading is rather overwhelming. I imagine that Luther may have formed his opinion while studying Augustine's discourses. It could have been from a single letter, or it could have been a conclusion he drew from several letters. It is entirely possible that there are some letters that illustrate exactly what he was quoted saying, though they may not yet be translated into English, or the specific references may have been left out because the translators considered the accusations "puerilities" or "rhetoric."