The Two Towers, “The White Rider”. Gandalf was bidden by Galadriel to give this messages to Aragorn.

Where now are the Dúnedain, Elessar, Elessar?
Why do thy kinsfolk wander afar?
Near is the hour when the Lost should come forth,
And the Grey Company ride from the North.
But dark is the path appointed for thee:
The Dead watch the road that leads to the Sea.

And this message to Legolas

Legolas Greenleaf long under tree
In joy thou hast lived. Beware of the Sea!
If thou hearest the cry of the gull on the shore,
Thy heart shall then rest in the forest no more.

Provided by: NenyaGold