We don't have the apostles with us today. The only way we can know the words of the apostles now is through Scripture, the parts of the Bible that some of them penned, as well as the parts of the Bible where their words are recorded. And 2 Timothy 3:16-17 says:
NKJV 2Ti 3:16 All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness,
2Ti 3:17 that the man of God may be complete, thoroughly equipped for every good work.
It doesn't say, "but if you're a Gentile, don't take any notice of words not spoken or written by Paul or Barnabas."