In String Quartet No. 8, Beethoven made use of a Russian theme based on the folk song (or hymn) "Glory To The Sun". Other composers also used this song as a theme: Mussorgski in "Boris Gudunov", Arenski in "String Quartet No. 2", Rachmaninoff in "6 Morceau for Piano Duet". (See Wikipedia article on Beethoven String Quartet No. 8.) According to the Wikipedia article, the original song was "recorded" (I think they mean in the sense of written down as sheet music) by Nikolay Lvov and Jan Prac.
Is there an accessible recording of the original song around? I could swear I found one on You Tube a few years ago, but now I can't find it.