Rather than look for an outside source (such as Q <ref>The Q document theory was created by Greek Greeks to try to understand why the gospels differ and why they are the same. They theorize that the gospel writers used a common text as their source. The gospek gospel writers did not write in a vacuum, requiring a source text to copy from. Matthew has the book of Mark. Luke had Mark and Matthew, and John had the other three.</ref>) for Mark, perhaps a closer look at the scriptures available to Peter in is order.