Gevurot Meyruach Hakodesh 20:28-31

Pay attention to yourselves and to all the Eder HASHEM (flock of G-d) in which the Ruach Hakodesh has placed you as mashgichim ruchaniyim (spiritual overseers) to do the work of ro'im (shepherds) over the Kehillah of HASHEM which Adoneinu purchased for the Geulah with his own dahm. I have da'as that after my departure savage ze'evim (wolves) will come in among you, not sparing the eder (flock). And from you yourselves will rise up anashim speaking perverted doctrines in order to draw away talmidim after themselves. Therefore, be shomer, remembering that for shloshah shanim, yomam v'lailah, I did not stop admonishing each one of you with tears.