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

Thus the Wise were troubled, but none as yet perceived that Curunír had turned to dark thoughts and was already a traitor in heart: for he desired that he and no other should find the Great Ring, so that he might wield it himself and order all the world to his will. Too long he had studied the ways of. Sauron in hope to defeat him, and now he envied him as a rival rather than hated his works. And he deemed that the Ring, which was Sauron's, would seek for its master as he became manifest once more; but if he were driven out again, then it would lie hid. Therefore he was willing to play with peril and let Sauron be for a time, hoping by his craft to forestall both his friends and the Enemy, when the Ring should appear.