Using one unnamed source was a mistake I made once. I was working for a small mom-and-pop newspaper. Remember, I wasn't trained as a reporter but even so I knew better. One day I was sent to interview our rep to the state house in MonkeyTown about the recent legislative session. I had not been paying attention and so really wasn't prepared. He saw this and saw an opportunity to string me along with a false story. I feel for it. He told me I couldn't name him as the source but gave me this song-and-dance about a company which would be moving into the area. The kicker was this company built trolley cars!!!!
I feel for it and convinced my editor to print a small blurb about the company. To teach me a lesson, the editor ran it on the front page and under my by-line. That was well over ten years ago. It still hurts. I imagine that I was laughed about in quite a few bull sessions later.
It is also a mistake I NEVER made again. The NYT does not show the same professionalism as Larry O. Glass, the editor of The North Jackson Progress.
You and your editor would have been justified in not just apologizing for the error but publically exposing the culprit's name. The contract you had w/him about not naming him was broken by HIM when he fed you a fake story.
You learned a valuable lesson which is still standing you in good stead.