UKC

Can anyone help me find this quote please? I vaguely remember it may from the intro to one of Messner's books, written by someone else.

The context was watching a mountain face, seeing a speck "moving impossibly fast", and then realising it was Messner descending back to camp.

It goes through my head often, I'd love to get it more accurate. I might be a million miles off in the context though.

TIA
Steve M