Is it permissible for a wife to fast the day of 'Arafah if she has sworn an oath not to observe voluntary fasts during her husband's lifetime?

It is commendable for a woman to observe voluntary fasts, such as the fast of the Day of Arafat, with her husband's permission. It is also commendable for her to break her oath to abandon something commendable, and she must offer expiation for breaking an oath (feeding ten poor people, or clothing them, or freeing a slave; or fasting three days if she cannot afford the aforementioned), based on the Almighty's saying: "And do not make [your oath by] Allah an excuse against being righteous and fearing Allah and making peace among people." Fasting is among righteousness and piety. The Prophet, peace and blessings be upon him, encouraged doing what is good and offering expiation for an oath.