The Ponymarillion II: Song of Starfall

Oath of Starfall (excerpt)

Taken by Luna and her sisters; led to the exile of the Alicorn race from the Undying Lands

The dreadful irrevocable oath taken by Starfall and her seven daughters.

Celestia followed them to Equestria but did not take part in the oath itself...

“Be she foe or friend, be he foul or clean

Brood of Tírek or sparkly Ponyta,

Unicorn or Pegasus, or follower, My Little Human

or Earth Pony, yet unborn upon Little-Equestria,

Neither law, nor love, nor magic of friendship

Danger of darkness, nor Doom itself

Shall defend thee from Starfall, and all of her kinship,

Whoso hideth or hoardeth or otherwise keepeth

An Element of Harmony from Alicorn hooves!

This swear we… Undying love and tolerance

we shall deal them ere Day’s ending,

Woe unto world’s end! Our word hear thou,

Faûst Allmother! To the everlasting Drama

Unfriendliness doom us if our deed faileth…

On the holy mountain Poniquetíl hear in witness

and our vow remember, Twilë, Shyavanna!"