§ Of Beren and Lúthien The Silmarillion

Then a winter, as it were the hoar age of mortal Men, fell upon Thingol. But Lúthien came to the halls of Mandos, where are the appointed places of the Eldalië, beyond the mansions of the West upon the confines of the world. There those that wait sit in the shadow of their thought. But her beauty was more than their beauty, and her sorrow deeper than their sorrows; and she knelt before Mandos and sang to him.