Lay of Leithian Canto V
This Canto speaks of Lúthien Tinúviel after the departure of Beren and how she went to her mother Melian and friend Dairon, begging for aid, from the first foresight and from the second music. Melian said that Beren was in the dungeons of Thû, and Dairon refused to play any music. A second time Dairon betrayed her, this time out of love, to her father Thingol, who placed her in a guarded treehouse. But by magic she grew out her hair and made a robe and rope of it "a magic dress/that all was drenched in drowsiness". Lowering the rope she put to sleep her guards and escaped.