§ Of the Coming of Men into the West The Silmarillion

The years of the Edain were lengthened, according to the reckoning of Men, after their coming to Beleriand; but at last Bëor the Old died when he had lived three and ninety years, for four and forty of which he had served King Felagund. And when he lay dead, of no wound or grief, but stricken by age, the Eldar saw for the first time the swift waning of the life of Men, and the death of weariness which they knew not in themselves; and they grieved greatly for the loss of their friends. But Bëor at the last had relinquished his life willingly and passed in peace; and the Eldar wondered much at the strange fate of Men, for in all their lore there was no account of it, and its end was hidden from them.