Three Rings for the Elven-kings under the sky,
Seven for the Dwarf-lords in their halls of stone,
Nine for Mortal Men doomed to die,
One for the Dark Lord on his dark throne
In the Land of Mordor where the Shadows lie.
One Ring to rule them all. One Ring to find them,
One Ring to bring them all and in the darkness bind them
In the Land of Mordor where the Shadows lie.'

...
'Nine he gave to Mortal Men, proud and great, and so ensnared them. Long ago they fell under the dominion of the One, and they became Ringwraiths, shadows under his great Shadow, his most terrible servants. Long ago. It is many a year since the Nine walked abroad. Yet who knows? As the Shadow grows once more, they too may walk again.'
...
'So it is now: the Nine he has gathered to himself; the Seven also, or else they are destroyed. The Three are hidden still. But that no longer troubles him. He only needs the One; for he made that Ring himself, it is his, and he let a great part of his own former power pass into it, so that he could rule all the others . If he recovers it, then he will command them all again, wherever they be, even the Three, and all that has been wrought with them will be laid bare, and he wi ll be stronger than ever.

(LoTR, I-2)

Over the lip of the little dell, on the side away from the hill, they felt, rather than saw, a shadow rise, one shadow or more than one. They strained their eyes, and the shadows seemed to grow. Soon there could be no doubt: three or four tall black figures were standing there on the slope, looking down on them. So black were they that they seemed like black holes in the deep shade behind them. Frodo thought that he heard a faint hiss as of venomous breath and felt a thin piercing chill. Then the shapes slowly advanced.
Terror overcame Pippin and Merry, and they threw themselves flat on the ground. Sam shrank to Frodo's side. Frodo was hardly less terrified than his companions; he was quaking as if he was bitter cold, but his terror was swallowed up in a sudden temptation to put on the Ring.
...
Immediately, though everything else remained as before, dim and dark, the shapes became terribly clear. He was able to see beneath their black wrappings. There were five tall figures: two standing on the lip of the dell, three advancing. In their white faces burned keen and merciless eyes; under their mantles were long grey robes; upon their grey hairs were helms of silver; in their haggard hands were swords of steel. Their eyes fell on him and pierced him, as they rushed towards him. Desperate, he drew his own sword, and it seemed to him that it flickered red, as if it was a firebrand.
Two of the figures halted. The third was taller than the others: his hair was long and gleaming and on his helm was a crown. In one hand he held a long sword, and in the other a knife; both the knife and the hand that held it glowed with a pale light. He sprang forward and bore down on Frodo.

At that moment Frodo threw himself forward on the ground, and he heard himself crying aloud: O Elbereth! Gilthoniel! At the same time he struck at the feet of his enemy. A shrill cry rang out in the night; and he felt a pain like a dart of poisoned ice pierce his left shoulder.

(LoTR, I-11)

'Look!' he cried; and stooping he lifted from the ground a black cloak that had lain there hidden by the darkness. A foot above the lower hem there was a slash. 'This was the stroke of Frodo's sword,' he said. 'The only hurt that it did to his enemy, I fear; for it is unharmed, but all blades perish that pierce that dreadful King. More deadly to him was the name of Elbereth.'

(LoTR, I-12)

He could see them clearly now: they appeared to have cast aside their hoods and black cloaks, and they were robed in white and grey. Swords were naked in their pale hands; helms were on their heads. Their cold eyes glittered, and they called to him with fell voices.
Fear now filled all Frodo's mind. He thought no longer of his sword. No cry came from him. He shut his eyes and clung to the horse's mane. The wind whistled in his ears, and the bells upon the harness rang wild and shrill. A breath of deadly cold pierced him like a spear, as with a last spurt, like a flash of white fire, the elf-horse speeding as if on wings, passed right before the face of the foremost Rider.

(LoTR, I-12)

`Then you knew of the Riders already-before I met them?'
'Yes, I knew of them. Indeed I spoke of them once to you; for the Black Riders a re the Ringwraiths, the Nine Servants of the Lord of the Rings. But I did not know that they had arisen again or I should have fled with you at once.

(LoTR, II-1)

The memory of words at the Council came back to me: words of Saruman, hal f-heeded at the time. I heard them now clearly in my heart.
` "The Nine, the Seven, and the Three," he said, "had each their proper gem. Not so the One. It was round and unadorned, as it were one of the lesser rings; but its maker set marks upon it that the skilled, maybe, could still see and read."

(LoTR, II-2)

But Sauron gathered into his hands all the remaining Rings of Power; and he dealt them out to the other peoples of Middle-earth, hoping thus to bring under his sway all those that desired secret power beyond the measure of their kind. Seven Rings he gave to the Dwarves; but to Men he gave nine, for Men proved in this matter as in others the readiest to his will. And all those rings that he governed he perverted, the more easily since he had a part in their making, and they were accursed, and they betrayed in the end all those that used them.
...
Men proved easier to ensnare. Those who used the Nine Rings became mighty in their day, kings, sorcerers, and warriors of old. They obtained glory and great wealth, yet it turned to their undoing. They had, as it seemed, unending life, yet life became unendurable to them. They could walk, if they would, unseen by all eyes in this world beneath the sun, and they could see things in worlds invisible to mortal men; but too often they beheld only the phantoms and delusions of Sauron. And one by one, sooner or later, according to their native strength and to the good or evil of their wills in the beginning, they fell under the thraldom of the ring that they bore and under the domination of the One, which was Sauron's. And they became for ever invisible save to him that wore the Ruling Ring, and they entered into the realm of shadows. The Nazgûl were they, the Ringwraiths, the Enemy's most terrible servants; darkness went with them, and they cried with the voices of death.

(Silm, OF THE RINGS OF POWER AND THE THIRD AGE)

Celebrimbor, desperate, himself withstood Sauron on the steps of the great door of the Mírdain; but he was grappled and taken captive, and the House was ransacked. There Sauron took the Nine Rings and other lesser works of the Mírdain; but the Seven and the Three he could not find. Then Celebrimbor was put to torment, and Sauron learned from him where the Seven were bestowed. This Celebrimbor revealed, because neither the Seven nor the Nine did he value as he valued the Three; the Seven and the Nine were made with Sauron's aid, whereas the Three were made by Celebrimbor alone, with a different power and purpose.

(UT, THE HISTORY OF GALADRIEL AND CELEBORN and of Amroth King of Lórie n)