
He died during that night of December 5, age 35. Schack tells us that Mozart himself sang the alto part but got only as far as the Lacrimosa, at which point he broke into tears and put the score aside.

His friend Benedikt Schack, the tenor who sang Tamino in The Magic Flute, relates that, on the afternoon before Mozart died, the composer had the unfinished manuscript of the Requiem brought to him in bed and sang through the vocal parts with several friends. By that time, however, he was seriously ill and needed to dictate some of his composition to an assistant. Toward the end of that year, after completing The Magic Flute and fulfilling a late commission for another opera, La Clemenza di Tito, Mozart was able to become fully engaged in writing his requiem. The secret patron behind the commission was Count Franz von Walsegg, who intended to pass off the work as his own composition in memory of his recently departed young wife. Mozart was offered a significant fee, half of it in advance, on the condition that it be anonymous. In mid-1791, when he was working on The Magic Flute, Mozart was visited by a stranger who commissioned him to write a requiem.
