In 1826, a year before his death, Ludwig van Beethoven completed his string quartet number 14 in C# minor, opus 131.
Although it was not well received by the general public upon its first performance, a rather large number of quite significant musicians seem to have thought highly of it in their time.
Beethoven String Quartet 14, Opus 131, first movement
When Schubert first heard the piece, he is reported to have said, “After this, what is left for us to write?” And as he lay dying, a year after Beethoven’s own death, Schubert asked for it to be played, and his closest friends obliged him. It was very possibly the last piece of music Schubert heard in his life.