From hour 1 minute 43 of episode 434 with Eliezer Yudkowsky and Nate Soares: https://www.samharris.org/podcasts/making-sense-episodes/434-can-we-survive-ai
Sam's full quote is:
"One thing that is almost guaranteed to emerge and will likely create a backlash is the dawn of an AI mediated religion. A proper cult organised around an AI oracle that gets enough traction it's going to alarm all the legacy religious people on earth and there's going to be a backlash."
Sam then goes on to describe it as "super-scientology organised around ChatGPT 7".
I gave a reasonably arbitrary 10 year time horizon for this.