Scripture. “Search the scriptures daily”! Paul’s writings became scripture per Peter.
” Paul’s writings became scripture per Peter.”
No, Paul’s writings were scripture because of where they came from (God) not because of Peter. Peter recognized they were scripture. The Jewish Bereans would not - until converted - believe Paul’s writings were scripture. And Paul had written very little at that point any way.
You can see this for yourself. Look at the left column here for Acts 17. Look at the middle column for “Galatians”: http://www.blueletterbible.org/study/paul/timeline.cfm I know timelines can differ because it’s largely guess work, but the idea is simple to understand. Paul wrote little or nothing before he dealt with the Bereans. He was explaining the Old Testament prophecies to them and they were checking the books (and their traditions about them as well since there were many) to see if he was right.