Die Schuldigkeit des ersten Gebots (complete title in historical spelling: Die Schuldigkeit Des ersten und fürnehmsten Gebottes; English: The Obligation of the First and Foremost Commandment), K. 35, is a sacred musical play (geistliches Singspiel) composed by Wolfgang Amadeus Mozart in 1767 when he was 11 years old. It is Mozart's first opera or, more specifically, sacred drama, as is suggested by the name. The libretto is now attributed to Ignaz Anton von Weiser, although Johann Adam Wieland or Jakob Anton Marianus Wimmer had been suggested earlier. (The title page of the libretto ascribes it only to "J.A.W.".)
Only the first part of the opera was composed by Mozart; the second and third parts were contributed by Michael Haydn and Anton Cajetan Adlgasser respectively. However, these other two parts have not survived.
Part I of the opera was first performed on March 12, 1767 in the Knight's Hall of the Palace of the Archbishop, Salzburg. Part II was performed on March 19, and Part III on March 26.