Tradition
St. Augustine
The Enarrations, or Expositions, on the Psalms
Psalm 133 › Section 4
4. Moreover, beloved, there are they who are false Monks, and we know men of this kind; but the pious brotherhood is not annulled, because of them who profess to be what they are not. There are false Monks, as there are false men among the Clergy, and among the faithful....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)