1 John 2:19 in the King James Version
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.
Context
18 Little children, these are the end times, and as you heard that the Antichrist is coming, even now many antichrists have arisen. By this we know that it is the final hour.
19 They went out from us, but they didn’t belong to us; for if they had belonged to us, they would have continued with us. But they left, that they might be revealed that none of them belong to us.
20 You have an anointing from the Holy One, and you all have knowledge.