Symphony No. 1 - Gustav Mahler
Gustav Mahler (1816-1911) was an Austrian composer whose musical styles spanned the Late Romantic and Early Modern periods.
Mahler’s first symphony (also known as “Titan”) was completed in 1888. This is the first instance of any symphony having muted parts, a recurring feature in some, but not all, Mahler symphonies. This symphony has a fourth trombone (fourth movement only, for reinforcement). This is another symphony first.
To learn more about the composer, visit Gustav Mahler on Wikipedia.
For more on the composition, visit Mahler Symphony No. 1 on Wikipedia.
Performance
Mahler: Symphony No. 1 - Staatskapelle Dresden & Fabio Luisi 2008
Excerpts
Mahler Symphony No. 1 audio excerpts with orchestra are available on tromboneexcerpts.org.
Trombone Parts and Score
Full score and orchestra parts for Mahler Symphony No. 1 are available on IMSLP.org.
NOTE: IMSLP provides access to public-domain scores and parts, with copyright status varying by country. Users are responsible for observing applicable copyright laws.
Trombone parts are available on IMSLP.org as follows:
Trombones 1 and 2 include sections in both tenor and bass clef. The third and fourth parts are in bass clef.
Ranges and clefs by Part

More Mahler
Trombone Resources playlist of Mahler with trombones in the instrumentation.
Trombone Resources is maintained by a lifelong trombonist with an interest in orchestral repertoire and primary sources.