§ Of Beren and Lúthien The Silmarillion

Now Carcharoth espied them from afar, and he was filled with doubt; for news had long been brought to Angband that Draugluin was dead. Therefore when they approached he denied them entry, and bade them stand; and he drew near with menace, scenting something strange in the air about them. But suddenly some power, descended from of old from divine race, possessed Lúthien, and casting back her foul raiment she stood forth, small before the might of Carcharoth, but radiant and terrible. Lifting up her hand she commanded him to sleep, saying: 'O woe-begotten spirit, fall now into dark oblivion, and forget for a while the dreadful doom of life.' And Carcharoth was felled, as though lightning had smitten him.