Yes, 'Ball Pythons' Barker and Barker 2006 vpi library pp 171
"Ball pythons that do not have food in their guts usually can tolerate low temperatures to 55ºF and highs to 100ºF for periods of several days."
They also comment that they would NEVER on purpose subject them (balls) to temps below 75 and above 90.
There is a reference about digestion and high low temps on page 172 they continue to speak about ambient air temps and ventilation as well as heat generated from digestion (I have noticed this as well) in smaller snakes.
There is also notes in "Clinical Anatomy and Physiology of Exotic Species" by O'Malay (or something ??) which I don't have in front of me, (library book)
I read an article by Klingenburg on digestion and temps of snake in general but I can't remember where that was exactly where that was a journal I think. I am 70% certain it was Klingenburg but I could be mistaken on that it was a while ago.
I would never suggest that a royal should ever be at 100º but short contact is not going to cause burns. It does have other health impacts that are also very critical. I don't know at what temperature burns will occur or what exact conditions need to be in place for a snake to burn its self, and I do know they happen with depressingly regularity.I do also believe that 100 for an hour or so is unlikely to do lasting damage.
(I have a pet theory on why, too low ambient temps, temperature sensing of snakes in general is crude more an average temp not exact temps, too low ambient temps and too high surface allows the snake to sit and burn. My idea, no reference just a unproven notion on my part)