It is mentioned in the Völuspá:
Stóð fyr norðan, / á Niðavöllom / salr úr gulli / Sindra ættar
(Stood before the north, a dark field, Halls of gold, Sindri's tribe,").
One interpretation of the above verse would read like this:
Before you reach the north (Niflheim being the world furthest to the north), A dark dwelling stands (The dwarf world), In halls of gold, Sindri's bloodline lives.
Sindri was a famous dwarf. And ættar means bloodline, or in this case most likely kin or tribe.
Niðavellir has often been interpreted as one of the Nine Worlds of Norse legend. The problem is that both Nidavellir and Svartalfheim are mentioned, and it is unclear if the sixth world is a world of dwarfs or one of dark elves.