He asked God for a sign on one day before he left a town on tour. He walked into Mall found out that they held mass in the basement(?). He walked into the chapel which had mass. Well after the mass he talked to the priest about the question from the book. He finds out its the author who is still living. A brusque old fashion priest in his late golden years.
It's been years I might be off on the accuracy. But if I remember that's the gist of it.
He repeated the anecdote in “Hail, Holy Queen.” The book in question was about the Assumption of Mary.