1 John 5:7

A previous response to a similar question passed along this information: “When Erasmus was publishing a NT text at the time of Luther, he did not have those verses [1 John 5:7-8] in any of the Greek manuscripts that were extant at the time. He said he would insert them only if a Greek text were found that included them. Apparently, a scribe forged a Greek document with those verses in the text, and Erasmus, not knowing that the document was forged, kept his promise to include them. But the evidence for 1 John 5:7-8 does not warrant their inclusion.” This concerns the third edition of Erasmus’ Greek New Testament in 1522.

Since Martin Luther and the translators of the King James Version both used the Greek New Testament published by Erasmus, the verses in question made their way into their translations.