I can't think of an example of maximum temperature but we can establish some baselines;
In the original Pokemon Red pokedex (for the Gameboy) it stated that:
Charizard, the Flame Pokémon. Charizard's powerful flame can melt
Taking this at face value, (and given that the element with the highest melting point is Tungsten) this would be 3500°C.
In one episode of the anime series (Volcanic Panic), Charizard and Magmar fight. Both end up covered in molten magma (approx 1000°C) and both attempt to flame each other with flames that are described as being similarly hot, with no effect.
In "Some Like It Hot!" (Magcargot! Getting the Hot Heart!!), Ash and crew encounter the Magcargo. The pokedex entry on Bulbapedia describes it thusly:
Magcargo's body temperature (18,000°F) is much higher than the
temperature of the surface of the sun (9,940°F).
When Ash encounters one, there's a brief discussion of which Pokemon he could use to attack it. Sensibly speaking, we can assume that Charizard would be able to resist it since Ash doesn't mention its weakness to the temperatures it can generate.