Origen of Alexandria (ca 185-254) may be the most brilliant Christian scholar and theologian of the patristic period. As a biblical critic he produced a critical edition of the OT in Hebrew/Greek versions called the Hexapla, composed several commentaries (see his commentaries on Matthew and John online) and was well aware of biblical discrepencies at the literal level including in the Gospels which his allegorical hermeneutic sought to transcend. His testimony on the fourfold Gospels is conventional and seems dependent on earlier authorities like Irenaeus and Clement. I cite the Greek and various online translations below (in Eusebius, Ecclesiastical History, 6.25.3-6). Eusebius goes on to cite Origen’s comments in his fifth book of his Exposition of John on other canonical writings and especially the identification of the author of the Gospel of John with the one who reclined on Jesus’ bosom (cf. John 13:23-5) and author of the Apocalypse (6.25.7-14) (for more on Origen’s canon see here).
ἐν δὲ τῷ πρώτῳ τῶν εἰς τὸ κατὰ Ματθαῖον, τὸν ἐκκλησιαστικὸν φυλάττων κανόνα, μόνα τεσσάρα εἰδέναι εὐαγγέλια μαρτύρεται, ὧδέ πως γράφων·ὡς ἐν παραδόσει μαθὼν περὶ τῶν τεσσάρων εὐαγγελίων, ἃ καὶ μόνα ἀναντίρρητά ἐστιν ἐν τῇ ὑπὸ τὸν οὐρανὸν ἐκκλησίᾳ τοῦ θεοῦ, ὅτι πρῶτον μὲν γέγραπται τὸ κατὰ τόν ποτε τελώνην, ὕστερον δὲ ἀπόστολον Ἰησοῦ Χριστοῦ Ματθαῖον, ἐκδεδωκότα αὐτὸ τοῖς ἀπὸ Ἰουδαϊσμοῦ πιστεύσασιν, γράμμασιν Ἑβραϊκοῖς συντεταγμένον· δεύτερον δὲ τὸ κατὰ Μάρκον, ὡς Πέτρος ὑφηγήσατο αὐτῷ, ποιήσαντα, ὃν καὶ υἱὸν ἐν τῇ καθολικῇ ἐπιστολῇ διὰ τούτων ὡμολόγησεν φάσκων, Ἀσπάζεται ὑμᾶς βαβυλῶνι συνελεκτὴ καὶ Μάρκος ὁ υἱός μου· καὶ τρίτον τὸ κατὰ Λουκᾶν, τὸ ὑπὸ Παύλου ἐπαινούμενον εὐαγγέλιον τοῖς ἀπὸ τῶν ἐθνῶν πεποιηκότα· ἐπὶ πᾶσιν τὸ κατὰ Ἰωάννην. (Greek text from Stephen Carlson)
In his first book on Matthew’s Gospel, maintaining the Canon of the Church, he testifies that he knows only four Gospels, writing as follows: Among the four Gospels, which are the only indisputable ones in the Church of God under heaven, I have learned by tradition that the first was written by Matthew, who was once a publican, but afterwards an apostle of Jesus Christ, and it was prepared for the converts from Judaism, and published in the Hebrew language. The second is by Mark, who composed it according to the instructions of Peter, who in his Catholic epistle acknowledges him as a son, saying, ‘The church that is at Babylon elected together with you, salutes you, and so does Marcus, my son.’ And the third by Luke, the Gospel commended by Paul, and composed for Gentile converts. Last of all that by John (Arthur Cushman McGiffert)<!—->
…but in the first of his [commentaries] on Matthew, defending the Church canon, he testifies of knowing only four gospels, writing something like this: as learned by tradition about the four gospels, which alone are incontested in the church of God under heaven, that, first, written was Matthew, once publican but later apostle of Jesus Christ, who published it for the believers from Judaism, composed in Hebrew letters; but second, Mark, who composed as Peter led him, whom he avowed as son in the catholic epistle, saying as follows: “She who is in Babylon, chosen together, sends you greetings and so does my son Mark” and third, Luke, who has composed for those from the Gentiles the gospel praised by Paul; after all of them, John. (Stephen Carlson)
… and in his first [book of his commentaries] on the [Gospel] according to Matthew, when defending the ecclesiastical canon, he testifies that he knows only four gospels, writing as follows: As [I have] learned in the tradition about the four gospels, which are alone uncontested in the church of God under heaven, namely, the first written was that according to the one-time tax collector but later apostle of Jesus Christ, Matthew, who published it for the believers from Judaism, composed in Hebrew characters; And second, that according to Mark, composed as Peter guided, whom he also proclaimed to be his son in the catholic epistle, speaking thus: “She that is in Babylon jointly chosen [with you] greets you, and my son Mark too.” And third, that according to Luke, the gospel praised by Paul, composed for those from the Gentiles. Finally, that according to John. (Bernard Orchard, The Order of the Synoptics, p. 169)
Now in the first of his [commentaries] on [the Gospel] according to Matthew, defending the ecclesiastical canon, [Origen] testifies to knowing only four gospels, writing somewhat as follows: … ‘having learned by tradition about the four gospels, which alone are undeniable in the church of God under heaven, that written first was that [Gospel] according to Matthew, who was at one time a taxcollector but afterwards an apostle of Jesus Christ. For those who came from Judaism came to believe, [Matthew] published it, composed in the Hebrew language. And second, the one according to Mark, as Peter guided him. In the Catholic Epistle he [Peter] also acknowledged him as a son through this assertion: “She who is in Babylon, chosen together with you, sends you greetings; and so does my son Mark.” And third, the one according to Luke, the Gospel commended by Paul for those who, from the Gentiles, [came to believe]. After them all, the one according to John.’ (C. Clifton Black, Mark: Images of an Apostolic Interpreter, p. 145)