Wedlock, Marriage (Nikaah)
Bukhari :: Book 7 :: Volume 62 :: Hadith 82
Narrated Abu Huraira:
The Prophet said, "It is not lawful for a woman (at the time of wedding) to ask for the divorce of her sister (i.e. the other wife of her would-be husband) in order to have everything for herself, for she will take only what has been written for her."