“The Lord hath made all things for himself: the wicked also for the evil day.”
“And the Lord said to Satan: Behold he is in thy hand, but yet save his life.”
“Be sober and watch: because your adversary the devil, as a roaring lion, goeth about seeking whom he may devour.”
“And no wonder: for Satan himself transformeth himself into an angel of light.”
I agree with every single one of those Scriptures...obviously. But not one says a born again believer can be demon possessed. Not one. You can search the Scriptures all day and you won’t find evidence of a believer being demon possessed.