I cannot provide you with a citation that would conclusively prove my point, anymore than you can provide me with a citation that would conclusively prove yours. Hence my common-sense proposition.

Gelasius was a pope of the fifth century. It is unreasonable to expect the standard of proof from such far-off times that we might reasonably expect of modernity. But my common-sense proposition does provide at least circumstantial evidence that Pope Gelasius did declare the doctrine a heresy. Are you independently minded enough to accept this?