Was He referring to the New Testament, which did not yet exist? Or is the Old Testament to be our guide?
Notice that He doesn't command us to settle intra-Christian disputes via Scripture.
"If he refuses to listen to them, tell it to the church; and if he refuses to listen even to the church, treat him as you would a pagan or a tax collector."
Only the masorite OT scriptures are completely reliable today. All that is derived from Greek texts has to be viewed as somewhat questionable.
As more and more Hebrew gospel ms are being discovered, the deliberate corruptions of the Greek gospels are becoming evident.
Christ disavowed all oral ‘tradition’ (takanot).