Extra-Biblical means outside of scripture and even opposed to it. This is different from something that is not found in scripture . Many things are not found in scripture. But anything that is extra to scripture has been added on , as being equal to scripture. This is the lie of many cults, including Roman Catholicism.
Scripture is finished and complete.
All else must be rooted in scripture, for this is our only Guide from God. Whatever does not accord with scripture is not of God, for God is always consistent with His own declared will. He cannot contradict Himself or change His mind. We must pray down the devil and crush his presence in our midst. Such a statement is founded on Dominion theory and other charismatic lies.