Eithel Nínui

After their escape from Angband with the Silmaril, Beren and Lúthien found themselves trapped before the gates of Morgoth's stronghold. Beren had lost his hand to Carcharoth the Wolf and was close to death, but he and Lúthien were rescued by Thorondor and his Eagles, who swooped down from the south and lifted them out of danger. As they flew from Angband, they were carried over the hidden valley of Tumladen where Gondolin stood, and legend said that Lúthien's tears for the wounded Beren fell on the green plain. There a fountain sprang from the ground, Eithel Nínui, the Fountain of Tinúviel, which gave out healing waters until the time of Gondolin's fall.

Eithel Nínui is not mentioned in the published Silmarillion, but it is found in the source texts of the story of the escape from Angband and the flight over Gondolin. The original text is reproduced in volume V of The History of Middle-earth (Part 2 VI, Quenta Silmarillion).