I have a old RSV its in that one, also in the NIV, Amplified, NASB, and the 1967 Schofield KJV. It is not in my 1769 edition of the Thompson chain, 1769 Scofield lll, or the NKJV.
Seems its pretty much in all of the newer translations, so its got to be an Alexandria error, you know the "best text".
Or possibly Westcott, and Hort.