§ Of Beren and Lúthien The Silmarillion

Therefore he summoned Beren, and even as Lúthien had spoken in the hour of his death they met again beyond the Western Sea. But Mandos had no power to withhold the spirits of Men that were dead within the confines of the world, after their time of waiting; nor could he change the fates of the Children of Ilúvatar. He went therefore to Manwë, Lord of the Valar, who governed the world under the hand of Ilúvatar; and Manwë sought counsel in his inmost thought, where the will of Ilúvatar was revealed.