Hi,
This is the first I've ever heard of the band doing a "prayer" before a songwriting session. I wouldn't say it's never happened before, or that I might've missed an interview somewhere. But for the most part, it seems like they just kind of go in an enter whatever it is they do. Anything that approaches a "spiritual" mark might come through the lyrical inspiration or process itself.
In a singular process of collaboration, U2 puts mood and emotion first. The words follow.
www.latimes.com
In terms of your own journey, I'm a songwriter myself. And for the most part, I find it better to sort of carve your own process rather than copying another one verbatim... or at the very least, taking that idea and sort of personalizing it your own situation and going from there. If you can't find the original source for the "prayer" mention, it might help going through articles like the one above, or the various books about the band talking about that sort of thing... and tailoring it to how you might go about it on your own.
Good luck! And welcome to the forum.