Acts
King James Version (KJV)

“For I know this, that after my departing shall grievous wolves enter in among you, not sparing the flock.”
King James Version (KJV)
20:29 Grievous wolves - From without, namely, false apostles. They had, not yet broke in on the Church at Ephesus.
Ac 20:29-31 Grievous wolves. The figure of the flock is still kept up. The "grievous wolves" were false teachers, and the special reference is to the Judaizing teachers, who taught that the Gentile Christians must keep the Jewish law. Paul's ministry was a long battle with the schismatics. See 1Ti 1:3,4,20; 2Ti 1:15 2:17. See also 3Jo 1:9,10. By turning to these references the names of some six of these "grievous wolves" will be found. Also in Revelation we learn that there were false teachers at Ephesus (Re 2:6).