§ Of Beren and Lúthien The Silmarillion

It is told in the Lay of Leithian how she escaped from the house in Hírilorn; for she put forth her arts of enchantment, and caused her hair to grow to great length, and of it she wove a dark robe that wrapped her beauty like a shadow, and it was laden with a spell of sleep. Of the strands that remained she twined a rope, and she let it down from her window; and as the end swayed above the guards that sat beneath the house they fell into a deep slumber. Then Lúthien climbed from her prison, and shrouded in her shadowy cloak she escaped from all eyes, and vanished out of Doriath.