For it is evident that the three Evangelists recorded only the deeds done by the Savior for one year after the imprisonment of John the Baptist and indicated this in the beginning of their account.… They say, therefore, that the apostle John, being asked to do it for this reason, gave in his Gospel an account of the period that had been omitted by the earlier Evangelists and of the deeds done by the Savior during that period; that is, of those that were done before the imprisonment of the Baptist. And this is indicated by him, they say, in the following words: "This was the beginning of the miracles that Jesus did"; and again when he refers to the Baptist, in the midst of the deeds of Jesus, as still baptizing in Aenon near Salim.… "For John was not yet cast into prison." John accordingly, in his Gospel, records the deeds of Christ that were performed before the Baptist was cast into prison, but the other three Evangelists mention the events that happened after that time.
Source: ECCLESIASTICAL HISTORY 3.24.8-12