§ Of Beren and Lúthien The Silmarillion

The hunters turned east and north, and following the course of the river they came at last upon Carcharoth the Wolf in a dark valley, down the northern side whereof Esgalduin fell in a torrent over steep falls. At the foot of the falls Carcharoth drank to ease his consuming thirst, and he howled, and thus they were aware of him, But he, espying their approach, rushed not suddenly to attack them. It may be that the devil's cunning of his heart awoke, being for a moment eased of his pain by the sweet waters of Esgalduin; and even as they rode towards him he slunk aside into a deep brake, and there lay hid. But they set a guard about all that place, and waited, and the shadows grew long in the forest.