It is believed that the composer of this work did not know the identity of its commissioner, and this composition was played at the funerals of Frederic Chopin and Franz Joseph Haydn.  
It is believed that the composer of this work did not know the identity of its commissioner, and this composition was played at the funerals of Frederic Chopin and Franz Joseph Haydn.  It includes a solo quartet in its Recordare and Tuba Mirum movements, while it also contains a notable Kyrie.  Its Sanctus and Benedictus movements were likely written by Franz Sussmayer.  For 10 points, identify this work, K626, that was left unfinished by its composer, a young Austrian prodigy.
It is believed that the composer of this work did not know the identity of its commissioner, and this composition was played at the funerals of Frederic Chopin and Franz Joseph Haydn.  
Requiem Mass in d minor by Wolfgang Amadeus Mozart [prompt on Requiem, accept Kochel No. 626 until mentioned]