Short answer
Yes. The words "the Father, the Word, and the Holy Ghost: and these three are one" were added to 1 John long after it was written. They are the only words in the Bible that name the Father, the Word and the Holy Ghost together and call them one. No Greek copy has them in its text before the fourteenth century. Every ancient translation except the Latin lacks them. The Greek church fathers never quoted them, even while they argued over the Trinity. The words first appear as part of the letter in a Latin book of the late fourth century. Erasmus left them out of his first two Greek New Testaments, then put them in during 1522 after critics attacked him. Most modern Bibles drop them. Islam teaches that God (﷾) is one, and the Qur'an tells Christians not to say "Trinity".
Full explanation
The verse as the King James Version prints it
The King James Version is the English Bible of 1611. Its verse 7 speaks of three that "bear record in heaven": the Father, the Word and the Holy Ghost. It adds that "these three are one". It took the verse from a printed Greek text that goes back to Erasmus, a Dutch scholar of the 1500s. This is the one place in the Bible where the Father, the Word and the Holy Ghost are named together and called one.
“For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one.”
What the Greek copies show
Bruce Metzger, the leading textual scholar of his generation, lists only eight Greek manuscripts (hand-written Greek copies) with the words. All eight are late, and four of them have the words only in the margin. The earliest with the words in its text is from the fourteenth or fifteenth century. Every ancient translation except the Latin lacks them. No Greek church father quotes them. Yet the fathers argued about the Trinity for most of the fourth century.
On 1 John 5:7-8, reports that the words about the Father, the Word and the Holy Spirit are absent from every known Greek manuscript except eight late ones, four of which have them written in the margin as a later addition; that no Greek church father quotes them; and that every ancient translation except the Latin lacks them.
Reports that the earliest known quotation of the words as part of 1 John is in a fourth-century Latin treatise, the Liber Apologeticus; that they are absent from the early Latin writers Tertullian, Cyprian and Augustine and from Jerome's Vulgate as first issued; that the earliest Greek manuscript with the words in its text (629) dates from the fourteenth or fifteenth century; and that they first appear in Greek in a Greek version of the acts of the Lateran Council of 1215. The words probably began as a note in the margin of Latin copies, reading the three witnesses of verse 8 as the Trinity, which later scribes copied into the text.
Where the words came from
The words first appear as part of 1 John in a Latin book of the late fourth century. They are not in the early Latin writers. They are not in Jerome's Vulgate, the Latin Bible, as he issued it. Scholars conclude the words probably began as a note in the margin of Latin copies. A reader took the three witnesses of verse 8 to mean the Trinity. Later copyists moved the note into the text. The words reached Greek only in the thirteenth century, translated from Latin.
Reports that the earliest known quotation of the words as part of 1 John is in a fourth-century Latin treatise, the Liber Apologeticus; that they are absent from the early Latin writers Tertullian, Cyprian and Augustine and from Jerome's Vulgate as first issued; that the earliest Greek manuscript with the words in its text (629) dates from the fourteenth or fifteenth century; and that they first appear in Greek in a Greek version of the acts of the Lateran Council of 1215. The words probably began as a note in the margin of Latin copies, reading the three witnesses of verse 8 as the Trinity, which later scribes copied into the text.
How the words entered printed Bibles
Erasmus published the first Greek New Testament to go on sale, in 1516. It left the words out, because no Greek manuscript he knew had them. Critics attacked him for this. Then a Greek copy made about 1520 was produced. He put the words into his third edition of 1522. From there they passed into the King James Version.
Recounts that Erasmus left the words about the three heavenly witnesses out of the first (1516) and second (1519) editions of his Greek New Testament, because he found them in no Greek manuscript. He was attacked for the omission, and put them into his third edition (1522) after a Greek manuscript containing them was produced. That manuscript had been copied about 1520, with the words taken from the Latin, and Erasmus himself suspected that its text had been altered to agree with the Latin; Metzger and Ehrman suggest the copy was made to order.
- Late 300s
In a Latin book
The words first appear as part of 1 John, in a Latin treatise.
- 1200s
Into Greek
The words reach Greek, translated from Latin.
- 1300s or 1400s
A Greek copy has them
The earliest Greek manuscript with the words in its text.
- 1516 and 1519
Erasmus leaves them out
His first two Greek New Testaments omit them: no Greek copy he knew had them.
- 1522
Erasmus puts them in
After critics attacked him and a Greek copy made about 1520 was produced.
- 1611
The King James Version
Prints the words, from the Greek text that goes back to Erasmus.
- 1881 on
Taken out again
The Revised Version and nearly every major translation since leave them out.
What modern Bibles do
Since the Revised Version of 1881, nearly every major translation has taken the words out. The Greek editions that translators use today leave them out too. The World English Bible shows verses 7 and 8 as the oldest manuscripts have them: three witnesses, the Spirit, the water and the blood. Isaac Newton, the English scientist, had already argued in 1690 that the verse was a corruption.
The English Revised Version (1881) and the American Standard Version (1901) removed the words about the Father, the Word and the Holy Ghost, and the RSV, NASB, NIV, NRSV and ESV print verse 7 without them, some with a footnote. The critical Greek editions used by translators today (Nestle-Aland and the United Bible Societies' text) leave them out.
“For there are three who testify: the Spirit, the water, and the blood; and the three agree as one.”
Isaac Newton, in a treatise sent to John Locke in 1690, traced the history of 1 John 5:7 through the manuscripts, versions and church writers, and argued that the words about the Father, the Word and the Holy Ghost were a later corruption of the text, as was "God" in 1 Timothy 3:16.
What the Qur'an says
The Qur'an tells the People of the Book (Jews and Christians) to say nothing of God (﷾) but the truth, and not to say "Trinity". The only verse that calls the Father, the Word and the Holy Ghost one was written into the Bible centuries after the letter. No writer of the Bible said it in those words. Islam teaches that God (﷾) is one.
“O People of the Book! Commit no excesses in your religion: Nor say of Allah aught but the truth. Christ Jesus the son of Mary was (no more than) a messenger of Allah, and His Word, which He bestowed on Mary, and a spirit proceeding from Him: so believe in Allah and His messengers. Say not "Trinity": desist: it will be better for you: for Allah is one Allah: Glory be to Him: (far exalted is He) above having a son. To Him belong all things in the heavens and on earth. And enough is Allah as a Disposer of affairs.”
Verse by verse
Cyprian, On the Unity of the Church 6 (c. 251)
Cyprian, bishop of Carthage, writes that the Lord says "I and the Father are one", and that it is written of the Father, the Son and the Holy Spirit, "and these three are one".
Cited for
Cyprian was quoting 1 John 5:7 about the year 251, so the verse must have been in his Bible.
The response
Cyprian names the Father, the Son and the Holy Spirit, not "the Word", as the verse does. In the Latin Bible, verse 8 about the Spirit, the water and the blood also ends "these three are one". Metzger explains the words as a reading of those three witnesses as the Trinity. The early Latin writers, Cyprian included, show no knowledge of the verse as the King James Version prints it.
Where it lands — Cyprian's sentence most likely reads verse 8 as the Trinity. It names the Son, not the Word, and it does not show that the added words were in his Bible.
1 John 5:7 — First Epistle of John, chapter 5, verse 7
“For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one.”
Cited for
The verse is in the King James Version and the Greek text behind it, so it is the word of God.
The response
The Greek text behind the King James Version goes back to Erasmus. He had no Greek manuscript with these words until one was made about 1520. The words are missing from every early Greek manuscript. They are also missing from every ancient translation except the Latin.
Where it lands — The verse is in the King James Version because of a sixteenth-century printed edition, not because the writer of the letter wrote it.
Perspectives
King James Only defenders
A minority of Christians hold that the King James Version and its Greek text are the preserved word of God. So they say the verse is genuine and modern Bibles have removed it.
The verse stands in the King James Version and the printed Greek text behind it.
Rebuttal
The verse is in the King James Version. But the Greek text behind it goes back to Erasmus, who knew no Greek manuscript with these words until one was made about 1520. The oldest Greek copies and every ancient translation except the Latin lack them.
Cyprian of Carthage, about 251, wrote of the Father, Son and Holy Spirit that "these three are one". They take this as a quotation of the verse.
Rebuttal
Cyprian names the Father, the Son and the Holy Spirit, not "the Word". The Latin text of verse 8 also ends "these three are one", so he most likely read verse 8 as the Trinity. Metzger finds the words absent from early Latin writers, Cyprian included.
Mainstream Christian scholarship
Most Christian scholars and churches accept that the writer of 1 John did not write the words. They hold that the Trinity is taught elsewhere in the Bible.
Christian textual scholars conclude the words are a later addition and the critical Greek text omits them.
Rebuttal
Islam agrees that the words are not original. Christians reply that the Trinity is taught elsewhere, as in Matthew 28:19. That verse names the three but does not say they are one God; the creeds spelled that out later. Constantinople in 381 set the Holy Spirit beside the Father and the Son in worship. The Qur'an says God (﷾) is one.
Where the academy stands
Status: Consensus
Textual scholars agree that the words about the Father, the Word and the Holy Ghost were not part of 1 John as first written. The Greek editions used by translators today omit them.
The Islamic perspective
The one verse that calls Father, Word and Holy Ghost one was added by later hands. The Bible's own manuscripts show what the Qur'an teaches: God (﷾) is one, and the Trinity was not the teaching of the prophets.
No Greek manuscript has the words in its text before the fourteenth century. Of the eight Metzger lists, four carry them only in the margin.
No Greek church father quotes the words, even in the fourth-century arguments over the Trinity. Yet they would have settled the question.
Every ancient translation except the Latin lacks the words. They first appear as part of the letter in a Latin work of the late fourth century.
Erasmus left the words out of his first two editions. He added them in 1522 only after a Greek copy made about 1520 was produced.
The Revised Version of 1881 and nearly every modern translation since have removed the words.
The Qur'an forbids saying "Trinity" and teaches that God (﷾) is one, with no son.