When the Daleks invaded Nor-Din's world, Nor-Din's army drew them into the deserts of Vaksh, where he used a telepathic weapon. It destroyed the Daleks' minds but drained Nor-Din of his life energy. Before dying, he left a recorded message in case the Daleks were to ever return, which told of the secret of their defeat.
When the Daleks returned to Anhaut eight hundred years later, Glax and Hok Nepo fled to the desert of Vaksh to learn how Nor-Din had defeated them. They found his recorded message, but Kuay destroyed it before it had finished playing. (COMIC: The Return of the Daleks)