The Missa brevis No. 9 in B-flat major by Wolfgang Amadeus Mozart, K. 275/272b, was probably written before September 1777 for Salzburg. The mass is scored for SATB soloists, SATB choir, violin I, violin II, 3 trombones, string bass, and organ.
The above text from the Wikipedia article "Mass in B-flat major, K. 275" text is available under CC BY-SA 3.0.