From Nick Strimple. Choral Music in the Nineteenth Century:
Ein deutsches Requiem became popular immediately. Most of Brahms’s close friends and family were present at one or another of the first performances, and many of them wrote to the composer poser expressing their deep sense of emotional fulfillment. The work was obviously close to Brahms’s heart, too, and he was not above expressing his ire when told of a performance planned by an inadequate choir in Hamburg:
My very esteemed sir: Permit these few hasty lines which surely seem permissible about a poor concert of your friend. You write: the perform[ance] of the Requiem is to “take place with the participation of the Bach-Society.”
Maybe that is just inadvertence, a slip of the pen!?
The planned perf makes sense only if it is an especially good one; heading the list for that is the choral group and we have every reason to be cautious.
The choral group for participation I found and still find most desirable is the Cecilia-Society. It did perform the R. less than a year ago and I am surely able to completely rely upon its choirmaster master Spengel. If that society either is unwilling or unable, then I would take a chance doing the thing with the combined theatre choruses of Hbg. and Schwerin-but it is really quite a lot to ask of these people for them, in addition to their daily chores, also to practice so difficult a piece, etc!
The Hbg. Bach-Society on the other hand never sang my R.-I need not describe to you at length how utterly impossible that outfit fit is!
I lack the time and this pointed steelpen makes writing almost impossible for me. But you can imagine what goes on at the Hamb. Choral Society: the Cecilian Society is the only one where they practice, etc.
I just hope you merely made a mistake as you were writing!!