We must observe, however, that in our good works we must sometimes avoid the offence of our neighbour, sometimes look down upon it as of no moment. For in as far as we can do it without sin, we ought to avoid the offence of our neighbour; but if a stumblingblock is laid before men in what concerns the truth, it is better to allow the offence to arise, than that the truth should be abandoned.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: in Faeceh., 1, Hom. 7