Who identifies the old shepherd as the man who spared the infant Oedipus?

The messenger from Corinth is he who identifies the shepherd as the one who had passed along the infant Oedipus. It's worth noting that the messenger himself does not seem to have known any of the intrigue that went along with the infant-switching, but merely that a baby was given him, which he then passed to the King and Queen of Corinth to raise.