2 John 1:8-9
8-9And be very careful around them so you don't lose out on what we've worked so diligently in together; I want you to get every reward you have coming to you. Anyone who gets so progressive in his thinking that he walks out on the teaching of Christ, walks out on God. But whoever stays with the teaching, stays faithful to both the Father and the Son.
10-11If anyone shows up who doesn't hold to this teaching, don't invite him in and give him the run of the place. That would just give him a platform to perpetuate his evil ways, making you his partner.