376AD -444AD: Cyril of Alexandria quoted all of 1 John 5:7-8 while quoting 1 John, chapter 5, verses 5, 6, 7, and 8 in 412-444AD: "And there are Three who give testimony in heaven, the Father, the Word, and the Holy Ghost. And these three are one. And there are three that give testimony on earth: the spirit and the water and the blood. And these three are one. ... (1 John 5:6-9)"... (Cyril of Alexandria, Thesaurus)

Greek:”· Ὅτι τρεῖς εἰσιν οἱ μαρτυροῦντες ἐν τῷ οὐρανῷ, ὁ Πατήρ, ὁ Λόγος, καὶ τὸ ἅγιον Πνεῦμα· καὶ οὗτοι οἱ τρεῖς ἕν εἰσι. Καὶ τρεῖς εἰσιν οἱ μαρτυροῦντες ἐν τῇ γῇ, τὸ Πνεῦμα καὶ τὸ ὕδωρ, καὶ τὸ αἷμα· καὶ οἱ τρεῖς εἰς τὸ ἐν εἰσὶν. ”(Cyril of Alexandria, Thesaurus; Migne Graeca, PG 75.616).

Cyril of Alexandria quoted 1 John 5:7-8 is an early proof that supports the KJB and also (interestingly) shows that even in Egypt both corrupt Alexandrian manuscripts and pure Byzantine manuscripts (wiith 1 John 5:7-8) were present and existed.

(Note: Of course, Alexandria, Egypt was full of Gnostic heresies that started with Origen, who made the wicked Septuagint from his Hexepla's fifth heresies, and Philo, another heretick.
Yet God preserved his words forever and still allows believers to have pure copies of Scripture even in bleak places despite any wicked heresies. So Cyril of Alexandria is still a valid witness to 1 John 5:7-8's authenicity, as he quoted all of 1John 5:6-9, including all of verses 7 and 8 [what critics call Johanneum Comma].)