Where from?

[BoromirTheBold]

Yes, it's in the FOTR. Part of the Song of Nimrodel that Legolas sang by the borders of Lorien:

'An Elven-maid there was of old,
A shining star by day:
Her mantle white was hemmed with gold,
Her shoes of silver-grey.

A star was bound upon her brows,
A light was on her hair
As sun upon teh golden boughs
In Lorien the fair.

Her hair was long, her limbs were white,
Adn fair she was and free;
And in teh wind she went as light
As leaf of linden-tree.

Beside the falls of Nimrodel,
By water clear and cool,
Her voice as falling silver fell
Into the shining pool.

Where now she wanders none can tell,
In sunlight or in shade;
For lost of yore was Nimrodel
And in the mountains strayed.

The Elven-ship in haven grey
Beneath the mountain-lee
Awaited her for many a day
Beside the roaring sea.

A wind by night in Northern lands
Arose, and loud it cried,
And drove the ship from Elven-strands
Across the streaming tide.

When dawn came dim the land was lost,
The mountains sinking grey
Beyond the heaving waves that tossed
Their plumes of blinding spray.

Amroth beheld the fading shore
Now low beyond the swell,
And cursed the faithless ship that bore
Him far from Nimrodel.

Of old he was an Elven-king,
A lord of tree and glen,
When golden were the boughs in spring
In fair Lothlorien.

From helm to sea they saw him leap,
As arrow from the string,
And dive into the water deep,
As mew upon the wing.

The wind was in his flowing hair,
The foam about him shone;
Afar they saw him strong and fair
Go riding like a swan.

But from the West has come no word,
And on the Hither Shore
No tidings Elven-folk have heard
Of Amroth evermore.'

If you have the 3-in-1 version of LOTR, it's on pages 330-332.