Mukhtasar Bukhari (Abridged) 1852 — Invalid conditions in marriage

Narrated by Sayyiduna Abu Huraira (may Allah be pleased with him) from the Noble Prophet (peace and blessings of Allah be upon him) that he (peace be upon him) said: "It is not permissible for a woman to ask her husband to divorce her sister (co-wife), so that she may pour out her share of the cup herself; this cannot be, she will get only what is destined for her."