The rumor was started by the site BadAssDigest at the San Diego Comic Con and quickly got out of hand. Read after the jump the site's explanation and reasons for it as well as the official denial by Disney and Lucasfilm...
The statement by Badassdigest:
This morning when writing about the potential new writers on Star Trek 3 I dropped a small rumor I had been hearing for months, and had repeated to me again at Comic-Con this weekend - that JJ Abrams was considering or threatening to pull out of Star Wars Episode VII, most likely because of disagreeing about where to shoot and being uncomfortable with the really tight development process (Disney wants the movie out in 2015). I buried the rumor at the end of the piece because I thought it was interesting and I keep wondering if Abrams dropped out of Star Wars would he go back to Star Trek. If. But if I thought the rumor had serious substance I would have, you know, made it its own article.
That rumor took on a life of its own. It's my fault; I didn't put enough disclaimers and weaselly language around the paragraph, and I should have been more specific with what I believe, which is that at this point it's unlikely Abrams will jump ship from Star Wars. It's not a winning move for him, and if he was going to do it he would have done it this spring, when I first heard the rumor. By this afternoon the little rumor - which other journalists and even industry types took to Twitter to say they had heard as well - had turned into sites reporting that Abrams was leaving Star Wars.
The official denial by Disney and Lucasfilm:
“There is no truth to the rumor. J.J. is having a great time working on the script and is looking forward to going into production next year.”