§ Of the Silmarils and the Unrest of the Noldor The Silmarillion

Now Fëanor's heart was still bitter at his humiliation before Mandos, and he looked at Melkor in silence, pondering if indeed he might yet trust him so far as to aid him in his flight. And Melkor, seeing that Fëanor wavered, and knowing that the Silmarils held his heart in thrall, said at the last: 'Here is a strong place, and well guarded; but think not that the Silmarils will lie safe in any treasury within the realm of the Valar!'