RC Sproul

“Frankly, the best manuscripts from antiquity do not include this story in the Gospel of John. The overwhelming consensus of textual critics is that it was not part of the original Gospel of John, at least not this portion of John. At the same time, the overwhelming consensus is that this account is authentic, it’s apostolic, and it should be contained in any edition of the New Testament. Whether it belongs here in John’s Gospel, in Luke’s Gospel (where some ancient manuscripts place it), or somewhere else is a question I leave for the ages. But I believe it is nothing less than the very Word of God, so I will treat it as such…”

Source: Commentary on John, 149 [emphasis added]