Additionally, 2 Peter 3:15–16 refers to Paul’s epistles as Scripture. Such a text testifies to the existence of a certain Pauline corpus which was also recognized, at least by some, as being authoritative.
So very early, even before the last canonical New Testament book was written, at least two groupings were already being recognized and referred to as authoritative. These were the Gospels and/or the tradition of Jesus’ oral teachings on the one hand and Paul’s epistles on the other. Such conclusions are also supported by a number of other very early sources as well.^25 Testimony of Apostolic Fathers