He played with famous people such as the violinists Carl Flesch , Szymon Goldberg , Joseph Wolfsthal and Jascha Heifetz , the composer and viola player Paul Hindemith and the pianist Artur Rubinstein . His musical collaborations during this time included violinists Carl Flesch , Szymon Goldberg , Joseph Wolfsthal and Paul Hindemith , who played the viola in a string trio with Feuermann and Wolfsthal . Other collaborators included Jascha Heifetz , William Primrose , and Arthur Rubinstein .