Peter called Paul's writing's..... wait for it.... writing's. That is the original meaning of the work "script" it means to write, or record.
The term scripture as something holy, came later. This is where knowledge of etymology comes in handy.
Greek - graphé - Definition: (a) a writing, (b) a passage of scripture; plur: the scriptures. [http://biblehub.com/greek/1124.htm]
Greek - graphé - used 51 times in the New Testament.
Matthew 21:4 Jesus said to them, "Did you never read in the Scriptures (graphé), 'THE STONE WHICH THE BUILDERS REJECTED, THIS BECAME THE CHIEF CORNER stone; THIS CAME ABOUT FROM THE LORD, AND IT IS MARVELOUS IN OUR EYES '?
Matthew 22:29 But Jesus answered and said to them, "You are mistaken, not understanding the Scriptures (graphé) nor the power of God.
Matthew 26:54 But how then should the Scriptures (graphé) be fulfilled, that it must be so?
Need I post them all? Peter called Paul's writings the same thing as Christ called scripture.