Whatever are you talking about? God Himself wrote the scriptures through men inspired by the Spirit. That is the ONLY source of truth by which we measure everything.
Man's right reason, created by God to glorify him, is not a source of truth?
Man doesn't have a "right reason". No one seeks after God-no, not one. Our hearts are wicked and deceitful in which we are cautioned to guard against. Now if you want to tell me that Aunt Agnes talked to God. And you're confident that she's a good source because she's a pretty nice lady who bakes cookies for the home groups, then perhaps we'll need to talk about this in more detail.
I'm pretty sure that none of the early fathers embraced a notion so manifestly false and contrary to Scripture.
I suggest you re-examine this notion. That is precisely why we have the Bible.
Sort of like the Constitution in political terms, where men in black robes are the ones who have the last say?
You said there that "The early church fathers rightfully understood that there is only one source of truth-the scriptures."
Of course, that is not true.
How would Abraham have received the truth when there wasn't one line of scripture written yet in his time?
Also, how would the scriptures themselves have been written if the "scriptures were the only source of truth" as you said. Where would the writers of the various documents of scripture have received the truth, if "the truth was only to be found in the scriptures", and if "the scriptures" as we know them today did not exist yet when they began writing their own "book(s)" of the Bible?
There had to be another "source of truth" besides the scriptures (and there was, and still is, and that "source of truth" is God).
The early Church fathers did not believe that statement you made in post #45, and neither should you.