You might be interested to learn that there is no illustration in the entire Bible of anyone casting demons out of a believer. The only people who ever legitimately cast out demons were Christ and the apostles. All the demon-possessed people they dealt with were unbelievers. Furthermore, they usually cast out demons totally apart from the will of the unbeliever. Jesus and the Twelve were exercising the gift of miracles. They were authenticating messianic and apostolic credentials, not establishing a pattern for us to follow.