In 1940, when organist and French Catholic mystic Olivier Messiaen (1908-92) was a prisoner in a German POW camp, he composed "Quartet for the End of Time." The quartet was written for violin, cello, piano and clarinet. Of the eight movements, only half feature all four instruments.
The fifth movement, "Praise to the Eternity of Jesus," features only cello and piano. He dispenses with a time signature and sets only a metronome marking for the 16th notes on the piano. Bar lines are somewhat random. The resolution at 5:36 is heartbreaking.
Messiaen: Quartet for the End of Time, 5th movement
The eighth movement is for violin and piano alone and is titled "Praise to the Immortality of Jesus." Here he uses a time signature while the piano imitates the beating of a heart. The violin soars above it, and at the end, triple pianissimo, the soul unites with Christ.
I had never heard of this composer before, but I like his music.
Some amazing art comes from suffering.
Not that anyone should have to go through such suffering, but there you go.