In the book by Tolkien the Silmarillion ,Maglor says...

[lathspell]

The Oath of Feänor:

Since you come with this question, I guess that you're in some way familiar with the Silmarillion.
Feänor is the one who made the Silmarils (the most reknowned work of the Elves), and he became proud of them, addicted you might say. After some time, he wouldn't show them to anyone anymore. When Melkor attacked Valinor with Ungoliant, slaying the Trees of Light, stealing the Silmarils and killing Finwë father of Feänor, Fëanor named Melkor 'Morgoth Bauglir', and swore an oath which many others swore after him. And as they swore it, they were under the doom of the Valar.

'Then Feänor swore a terrible oath. His seven sons leapt straightway to his side and took the selfsame vow together, and red as blood shone their drawn swords in the glare of the torches. They swore an oath which none shall break, and none should take, by the name even of Ilúvatar, calling the Everlasting Darkness upon them if they kept it not; and Manwë they named in witness, and Varda, and the hallowed mountain of Taniquetil, vowing to pursue with vengeance and hatred to the end of the World Vala, Demon, Elf or Man as yet unborn, or any creature, great or small, good or evil, that the time should bring forth unto the end of days, whoso should hold or keep or take a Silmaril from their possession.'

I hope this answers your question.

greetings,
lathspell