I've blogged about this before, but I thought I'd add a quote from Bart Ehrman about how the story of Jesus letting the adulterer go free (which is one of the most famous stories in the New Testament), is a well known interpolation. From Misquoting Jesus:
The story of Jesus and the woman taken in adultery is arguably the best-known story about Jesus in the Bible; it certainly has always been a favorite in Hollywood versions of his life. It even makes it into Mel Gibson's The Passion of the Christ, although that movie focuses only on Jesus's last hours (the story is treated in one of the rare flashbacks). Despite its popularity, the account is found in only one passage of the New Testament, in John 7:53-8:12, and it appears not to have been original even there.
Despite the brilliance of the story, its captivating quality, and its inherent intrigue, there is one other enormous problem that it poses. As it turns out, it was not originally in the Gospel of John. In fact, it was not originally part of any of the Gospels. It was added by later scribes.
How do we know this? In fact, scholars who work on the manuscript tradition have no doubts about this particular case. Later in this book we will be examining in greater depth the kinds of evidence that scholars adduce for making judgments of this sort. Here I can simply point out a few basic facts that have proved convincing to nearly all scholars of every persuasion: the story is not found in our oldest and best manuscripts of the Gospel of John; 18 its writing style is very different from what we find in the rest of John (including the stories immediately before and after); and it includes a large number of words and phrases that are otherwise alien to the Gospel. The conclusion is unavoidable: this passage was not originally part of the Gospel. (pp. 63-65)
The search feature on my blog sucks, and the previous post about this interpolation never comes up, so I'm hoping this post fixes that.