This is from a book written by an early Christian Church father named Irenaeus and is the earliest known reference to the four-fold gospel. Here, he's arguing against the questions being raised about the reasoning behind four Gospels being the number chosen and not more or less because at the tome there were dozens and dozens of Gospels floating around the Mediterranean. Interesting to see the magical thinking behind his argument. The number four, five, seven twelve and thirty were powerful magical numbers to these very superstitious people.
8. It is not possible that the Gospels can be either more or fewer in number than they are. For, since there are
four zones of the world in which we live, and
four principal winds, while the Church is scattered throughout all the world, and the “pillar and ground” of the Church is the Gospel and the spirit of life; it is fitting that she should have
four pillars, breathing out immortality on every side, and vivifying men afresh. From which fact, it is evident that the Word, the Artificer of all, He that sitteth upon the cherubim, and contains all things, He who was manifested to men, has given us the Gospel under
four aspects, but bound together by one Spirit. As also David says, when entreating His manifestation, “Thou that sittest between the cherubim, shine forth.” For the cherubim, too, were
four-faced, and their faces were images of the dispensation of the Son of God. For,
says, “The first living creature was like a lion,” symbolizing His effectual working, His leadership, and royal power; the second was like a calf, signifying sacrificial and sacerdotal order; but “the third had, as it were, the face as of a man,”—an evident description of His advent as a human being; “the fourth was like a flying eagle,” pointing out the gift of the Spirit hovering with His wings over the Church. And therefore the Gospels are in accord with these things, among which Christ Jesus is seated. For that according to John relates His original, effectual, and glorious generation from the Father, thus declaring, “In the beginning was the Word, and the Word was with God, and the Word was God.”
bla bla bla...
From the book 'Against Heresies' by Irenaeus of Lyonsc 175-185 CE