Eusebius - quoting Papias, the bishop of Heirapolis (130 AD)

"The Elder (the Apostle John) used to say this also; 'Mark, having been the interpreter of Peter, wrote down accurately all that he (Peter) mentioned, whether sayings or doings of Christ, not, however, in order. For he was neither a hearer nor a companion of the LORD; but afterwards, as I said, he accompanied Peter, who adapted his teachings as necessity required, not as though he were making a compilation of the sayings of the LORD. So then Mark made no mistake, writing down in this way some things as he (Peter) mentioned them; for he paid attention to this one things, not to omit anything that he had heard, not to include any false statement among them.'"

Eusebius - Ecclesiastical History III.39