In 1867 Adolf Jellinek published the following anecdote in the Viennese periodical Die Neuzeit (#46) about the recently deceased Galician scholar, Prague's Chief Rabbi Solomon J. Rapoport (Shir, 1790-1867). I haven;t seen the original, but it was translated into French and published under the title Un Officier er R. Saadia Gaon (pp. 1136-36 in Archives israélites Vol. 28, December of the same year. If your French is up to par, you can read it. If not, below is R. Sabato Morais's English translation as it appeared in the July 2, 1869 issue of the Jewish Messenger:
Obviously this is just a story; see Morais's note on the side. In Bernfeld's Toldos Shir pg. 8 he puts it this way: לא נדע אם ממקור נאמן שאכם או הם רק ספורי אגדה.