§ Of the Rings of Power and the Third Age The Silmarillion

To this Curunír now assented, desiring that Sauron should be thrust from Dol Guldur, which was nigh to the River, and should have leisure to search there no longer. Therefore, for the last time, he aided the Council, and they put forth their strength; and they assailed Dol Guldur, and drove Sauron from his hold, and Mirkwood for a brief while was made wholesome again.