The Requiem was finished (except for the 5th movement, which was added after the premiere) in the fall of 1866. Brahms showed it to Clara Schumann, and she said of it, “It has given me unspeakable joy.” But she also pointed out a problem: “The only really troublesome thing in it is the fugue with the pedal note.” And indeed, the fugue at the end of the 3rd movement is a source of much anxiety for every performer of the work.
The first three movements of the Requiem were performed in Vienna in December of 1867 (before the premiere of the entire work in April 1868). Eduard Hanslick wrote in his review: “While the first two movements of the Requiem, in spite of their somber gravity, were received with unanimous applause, the fate of the third movement was very doubtful…During the concluding fugue of the third movement, surging above a pedal-point on D, [one] experienced the sensations of a passenger rattling through a tunnel in an express train.”
Brahms would not consider changing the fugue; he felt the pedal was “an expression of the assurance in the text: ‘The souls of the righteous are in the hands of God and no torment shall touch them.’” (Jan Swafford Johannes Brahms)