As conductors of other composers' music, Mendelssohn, Berlioz, and Wagner professed the desire to be faithful in some sense to the conducted work, but each understood this fidelity differently. Mendelssohn and Berlioz saw performance as recreative, while Wagner was the first to regard it as a creative or interpretive act.
Bowen, Jose Antonio
"Mendelssohn, Berlioz, and Wagner as Conductors: The Origins of the Ideal of "Fidelity to the Composer","
Performance Practice Review:
1, Article 4.
Available at: https://scholarship.claremont.edu/ppr/vol6/iss1/4