Acts 19

There seven sons of a high priests saw that Paul was healing and casting out demons, even a cloth that touched him could be brought to the sick and they were healed.  These sons then tried to cast out a spirit by saying, "I adjure you by the Jesus whom Paul proclaims."  The spirit then replied, "Jesus I know, and Paul I recognize, but who are you?"  The man then attacked and overpowered the brothers.  We must beware for not every one who teaches with Jesus' name is a follower.  those brothers were wolves in sheep's clothing.