http://quod.lib.umich.edu/cgi/l/luther/luther-idx?type=DIV2&byte=4456364 gives Romans 3:28 as
So halten wir nun dafür, daß der Mensch gerecht wird ohne des Gesetzes Werke, allein durch den Glauben.
Allein.
What’s my beef?
Even though it is not in most English translations, many act as if it were there.
You see, I don't know the answer and I am looking for an "official" one.