1 John 2:19; 1 John 4:1

1 John 2:19

19 They went out from us, but they were not of us; for if they had been of us, they would no doubt have continued with us: but they went out, that they might be made manifest that they were not all of us.

1 John 4:1

1 Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world.