Damn! I came in here to say that it either happened in the novelization of “All Good Things” or “Q Squared”.
I actually have John de Lancie performing Q-Squared: the only audio I’ve ever purchased online form iTunes. It’s not that bad. Q is written perfectly in character (unlike certain Voyager episodes). And I’m a big fan of multiple universe stories, as well as stories that fix plotholes from the series. And, or course, de Lancie’s voice acting for the characters is superb.
I at one point had an ebook of the novel itself, but I haven’t been able to find it. I know there are a few things in it not in de Lancie’s version–for one thing, the story is not written from Q’a perspective, but from a semi-omniscient narrator (which is why changing it to Q works so well).
Sounds Buddhist. 
Anyway, another fun fact? The original Mary Sue was actually from a Star Trek fan story! From a fanzine in 1973.
But yeah, a number of the Star Trek novels were pretty good. Diane Duane’s Dark Mirror, for one. The audiobook was even read by de Lancie, though Q wasn’t in the story. Really an eye-opener to the man’s acting talents—he was always good as Q, but now I regret that he was only Q on the show.
I used to go through those books like popcorn—I fell out of it around the time they started publishing less stand-alone novels and more multi-part crossover tie-in books. I had my limits. 
I fell out when I discovered well written fanfiction–even a series that fixed Voyager’s crappy ending. (Yes, I am a fan, although I still see the flaws. It being Star Trek was sufficient.)