Peter Calls Paul Scripture

One of the earliest pieces of evidence for a New Testament canon is a throwaway remark.
Peter writes that Paul "wrote to you according to the wisdom given him, as he does in all his letters." Two things sit in that sentence. There is a collection - all his letters, known well enough to be referred to as a body. And it is being handled as a recognised authority.
Then the next clause: some things in them are hard to understand, "which the ignorant and unstable twist to their own destruction, as they do the other Scriptures."
The other Scriptures. Paul's letters are being grouped with them, casually, as though the point needed no argument.
Paul does something similar - quoting Deuteronomy and then a line of Luke's Gospel, and calling both "the Scripture says."
Scripture links:
- 2 Peter 3:15-16 - "as they do the other Scriptures."
- 1 Timothy 5:18 - "The Scripture says... 'The labourer deserves his wages.'"
- Luke 10:7 - the line Paul quotes as Scripture.
- Colossians 4:16 - letters circulated between churches.
The category was already in use inside the New Testament.