The Silmarillion

Farewell sweet earth and northern sky
for ever blest, since here did lie
and here with lissome limbs did run
beneath the Moon, beneath the Sun,
Lúthien Tinúviel
more fair than mortal tongue can tell.
Though all to ruin fell the world
and were dissolved and backward hurled
unmade into the old abyss,
yet were its making good, for this—
the dusk, the dawn, the earth, the sea—
that Lúthien for a time should be.

Then Morgoth looking upon her beauty conceived in his thought an evil lust, and a design more dark than any that had yet come into his heart since he fled from Valinor. Thus he was beguiled by his own malice, for he watched her, leaving her free for a while, and taking secret pleasure in his thought. Then suddenly she eluded his sight, and out of the shadows began a song of such surpassing loveliness, and of such blinding power, that he listened perforce; and a blindness came upon him, as his eyes roamed to and fro, seeking her.

This doom she chose, forsaking the Blessed Realm, and putting aside all claim to kinship with those that dwell there; that thus whatever grief might lie in wait, the fates of Beren and Lúthien might be joined, and their paths lead together beyond the confines of the world. So it was that alone of the Eldalië she has died indeed, and left the world long ago. Yet in her choice the Two Kindreds have been joined; and she is the forerunner of many in whom the Eldar see yet, though all the world is changed, the likeness of Lúthien the beloved, whom they have lost.

But Thingol perceived their hearts, and saw well that desiring the Silmaril they sought but a pretext and fair cloak of their true intent; and in his wrath and pride he gave no heed to his peril but spoke to them in scorn, saying: ‘How do ye of uncouth race dare to demand aught of me, Elu Thingol, Lord of Beleriand, whole life began by the waters of Cuiviénen years uncounted ere the fathers of the stunted people awoke?’

Then the lust of the Dwarves was kindled to rage by the words of the King; and they rose up about him, and laid hands on him, and slew him as he stood.