Answer:
I choose the scandal Jack Kelley and USA Today, 2004 as the basis for the answer.
At that time, Jack Kelley was a pretty well known journalist who gained his fame from writing articles about criminal activities that usually goes unnoticed by the public.
He mentioned in his articles that he obtained his information from a group of "anonymous sources" that he refused to show because of a 'threat to their safety'. In 2004, it was proven that he fabricated large portion of his anonymous sources.
If I were in his position, I wouldn't made the same choice. I will actually seek for whistleblowers who were willing to speak out about this issue. Given reward and anonymity that can be provided by big news organization, it's still very much possible to obtain the source without fabricating it.
