Beren And Luthien

But wandering in the summer in the woods of Neldoreth Beren came upon Lúthien, daughter of Thingol and Melian, at a time of evening under moonrise, as she danced upon the unfading grass in the glades beside Esgalduin. Then all memory of his pain departed from him, and he fell into an enchantment; for Lúthien was the most beautiful of all the children of Ilúvatar.

The silmarrilion the Tale of Beren and Lúthien.