The slow second part of the string quartet in A minor op. 29 gives the quartet its name: Rosamunde. A year before, in 1823, Schubert wrote incidental music for the play Rosamunde. The full name is Rosamunde, Fürstin von Zypern. That complete play takes about five hours, so the music is almost never performed in it’s entirety. It is mostly remembered for this: the string quartet in A minor.
Interestingly, at this time Schubert also wrote his famous Death and the Maiden quartet, in which he is quoting from one of his ever popular songs. It is quite easy to find this kind of self plagiarising in musical history. If a song is popular, why not use it again? It might also have been asked: not everyone had the chance to see the play, so seeing this short version of it might have attracted a new audience.