I read this in a pulp magazine (Analog or Galaxy), I think. In it an atheist telepath is asked to confirm that in his death throes, a saint had never despaired and thus still deserved canonization. He goes along for the money, figuring he'd make up a story. Instead he finds that, because of an instant of doubt, the subject was sentenced to eternal damnation, and that far worse waits for nearly everyone else. Unable to cope with the enormity of the message, he makes up a story of the subject's ascent into heaven.
Distinct memory that that the source was a pulp magazine, but not at all certain which one. It's at least thirty years ago, and probably closer to 40. I wish I could remember more details!