Melkor Returns.. - The Prophecy of Mandos
The Shaping of Middle Earth:
"This was the judgement of the Gods, when Eonwë and the sons of the Valar had returned unto Valmar: thereafter the Outer Lands should be for Mankind, the younger children of the world; but to the Elves alone should the gateways of the West stand ever open; and if they would not come thither and tarried in the world of Men, then they should slowly fade and fail. This is the most grievous of the fruits of the lies and works that Morgoth wrought, that the Eldalië should be sundered and estranged from Men. For a while his Orcs and his Dragons breeding again in dark places affrighted the world, and in sundry regions do so yet; but ere the End all shall perish by the valour of mortal Men.
But Morgoth the Gods thrust through the Door of Timeless Night into the Void, beyond the Walls of the World; and a guard is set for ever on that door, and Eärendel keeps watch upon the ramparts of the sky. Yet the ties that Melkor, Moeleg the mighty and accursed, Morgoth Bauglir the Dark Power Terrible, sowed in the hearts of the Elves and Men have not all died, and cannot by the Gods be slain, and they live to work much evil even to this later day. Some say also that Morgoth at whiles secretly as a cloud that cannot be seen or felt, and yet is venomous, creeps back surmounting the Walls and visiteth the world; but others say that this is the black shadow of Sauron, who served Morgoth and became the greatest and most evil of his underlings; and Sauron escaped from the Great Battle, and dwelt in dark places and perverted Men to his dreadful allegiance and his foul worship.
After the triumph of the Gods, Eärendel sailed still in the seas of heaven, but the Sun scorched him and the Moon hunted him in the sky. Then the Valar drew his white ship Wingelot over the land of Valinor, and they filled it with radiance and hallowed it, and launched it through the Door of Night. And long Eärendel set sail into the starless vast, the Silmaril upon his brow, voyaging the Dark behind the world, a glimmering and fugitive star. And ever and anon he returns and shines behind the courses of the Sun and Moon above the ramparts of the Gods, brighter than all other stars, the mariner of the sky, keeping watch against Morgoth upon the confines of the world. Thus shall he sail until he sees the Last Battle fought upon the plains of Valinor."
"Thus spake the prophecy of Mandos, which he declared in Valmar at the judgement of the Gods, and the rumour of it was whispered among all the Elves of the West: when the world is old and the Powers grow weary, then Morgoth shall come back through the Door out of the Timeless Night; and he shall destroy the Sun and the Moon, but Eärendel shall come upon him as a white flame and drive him from the airs. Then shall the last battle be gathered on the fields of Valinor. In that day Tulkas shall strive with Melkor, and on his right shall stand Eonwë and on his left Túrin Turambar, son of Húrin, Conqueror of Fate, coming from the halls of Mandos; and it shall be the black sword of Túrin that deals unto Melkor his death and final end; and so shall the Children of Húrin and all men be avenged."
"Thereafter the Earth shall be broken and re-made, and the Silmarils be recovered out of sea and earth and air; for Eärendil shall descend and yield up that flame that he hath had in keeping. Then Fëanor shall bear the Three and yield their fire to rekindle the Two Trees, and a great light shall come forth; and the Mountains of Valinor shall be leveled, so that the light goes out over all the world. In that light the Gods will again grow young, and the Elves awake and all their dead arise, and the purpose of Ilúvatar be fulfilled concerning them. But of Men in that day the prophecy speaks not, save of Túrin only, and him it names among the sons of the Gods."
(an explanation of Túrin's stay in Mandos)
The Book Of Lost Tales 2:
Turambar and the Foalókë:
"Then Húrin departed, but would not touch the gold, and stricken in years he reached Hisilómë and died among Men, but his words living after him bred estrangement between Elves and Men. Yet it is said that when he was dead his shade fared into the woods seeking Morwen, and long those twain haunted the woods about the fall of Silver Bowl bewailing their children. But the Elves of Kôr have told, and they know, that at last Húrin and Morwen fared to Mandos, and Nienor was not there nor Túrin their son. Turambar indeed had followed Nienor along the black pathways to the doors of Nienna, but Nienna would not open to them, neither would Mandos. Yet now the prayers of Húrin and Morwen came even to Manwë, and the Gods had mercy on their unhappy fate, so that those twain Túrin and Nienor entered into Fôs' Almir, the bath of flame, even as Arien and her maidens had done in ages past before the first rising of the Sun, and so were all their sorrows and stains washed away, and they dwelt as shining Valar among the blessed ones, and now the love of that brother and sister is very fair; but Turambar indeed shall stand beside Eonwë in the Great Wrack, and Melkor and his drakes curse the sword of Mormegil."