Ludwig van Beethoven's use of Russian folk songs in his compositions is indeed a fascinating aspect of his work. One notable piece where he incorporated a Russian folk song is in his "String Quartet No. 13 in B-flat major, Op. 130."
In the final movement of this string quartet, Beethoven included a section known as the "Alla danza tedesca" (German Dance) which contains a melody reminiscent of a Russian folk tune. It's believed that this melody was inspired by a Russian folk song that Beethoven heard or encountered during his lifetime.
Beethoven's use of folk elements, including Russian folk tunes, reflects his interest in incorporating diverse musical influences into his compositions, showcasing his innovative approach to music and his willingness to draw from various cultural sources to create unique and captivating works.