It is generally accepted that Mark the Evangelist based his presentation of the Gospel on the preaching of Peter. Eusebius of Caesarea, writing in the fourth century, related what Papias, a Christian in the early second century, said what he heard from John the Elder about Mark:
“And the elder used to say this, Mark became Peter’s interpreter and wrote accurately all that he remembered, not, indeed, in order, of the things said and done by the Lord.
For he had not heard the Lord, nor had followed him, but later on, followed Peter, who used to give teaching as necessity demanded but not making, as it were, an arrangement of the Lord’s oracles, so that Mark did nothing wrong in thus writing down single points as he remembered them. For to one thing he gave attention, to leave out nothing of what he had heard and to make no false statements in them.” (Historia Ecclesiastica, 3.39.15)
And thus the vivid narratives in Mark as if he was there by himself. Or, in this case, as if he told the stories as narrated by an eyewitness of the events. And hence we read how Jesus took Peter’s mother-in-law by hand and lifted her up (Mrk 1.31), how Peter said emphatically that he would not deny Jesus (14.31), the graphical details of Peter’s denial of Jesus (14.66-72, e.g., only in Mark that the rooster crowed twice, a difficulty which was recognized by both Matthew and Luke such that they edited it into once only — and a later scribe which added ‘and the rooster crowed’ in v. 68 to harmonize the story), etc.
And, finally, on how the young man sitting on the right side of the tomb of Jesus said to Mary Magdalene and Mary the mother of Jesus, “But go, tell his disciples and Peter that he is going before you to Galilee. There you will see him, just as he told you.” (16.7) The saying which was edited by Matthew to become as follow, ‘[T]ell my brothers to go to Galilee, and there they will see me.’ (Mat 28.10)