"Lalla-Rookh: An Oriental Romance" was a long narrative work, part prose and part poetry, by Thomas Moore, published in 1817. Lalla-Rookh was the name of the heroine in the story.

You can view the entire work at Google Book Search. It is 335 pages in that edition.

Several musical works were based on Moore's book, or on parts of it:
an opera ("Lalla Rookh," 1821) by Gaspare Spontini,
an oratorio ("Paradise and the Peri," Op. 50, 1843) by Robert Schumann,
a ballet ("Lalla Rookh," 1846) by Cesare Pugni,
an opera ("Lalla Roukh," 1862) by Félicien-César David,
an opera ("Feramors," 1863) by Anton Rubenstein,
a cantata ("Lalla Rookh," 1877) by Frederic Clay,
an opera ("The Veiled Prophet of Khorassan," 1881) by Charles Villiers Stanford,
an opera ("Zelica," 1891) by Stephen R. Philpot,
a cantata ("The Fire Worshippers", 1892) by Granville Bantock,
-- did I miss any?

Other things named Lalla Rookh include at least two sailing ships, a steam locomotive, and a settlement in Western Australia. There is also a Colorado-based band named Lalla Rookh that plays Scottish music.

However, I'm reasonably certain that what the original requestor wanted was this song recorded by Fairport Convention (I am only able to provide two brief excerpts from sound samples):

LALLA ROOKH
Words, Chris Leslie. Music, Maartin Allcock.

...through the water.
The figurehead will guard our crew,
For Lalla Rookh she is a princess of old India.
She looks ahead for storm or....

...the gulls no longer circle round us.
The sun is strong upon my face.
We're pulling hard upon her ropes now.
We hope this wind will last for days.
For Lalla Rookh....