All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all of his family and companions.
The ruling on Wife’s fast without the husband’s permission differs according to its type:
First: If fasting was obligatory; such as taking a vow to fast or making up the missed fasts since previous Ramadan and before the arrival of the next one due to the short period of time (short-term make up), in this case, the wife isn’t obliged to take her husband’s permission to fast nor he is permitted to prevent her. In this regard, it is stated: ”The wife is permitted to fast without the permission of the husband if her fasting was obligatory or was made to fulfill a vow and the latter isn’t permitted to prevent her from fasting in this case.” [Hashyat Al-Jamal]. Yet, if she had a plenty of time for making up missed fast since previous Ramadan and before the arrival of the next one(long-term make up) then she is obliged to ask for his permission.
Second: there are two cases in case her fast was voluntary as follows:
The first case: A fast that reoccurs more than once a year; such as fasting Mondays, Thursdays and the white days. In this case she isn’t permitted to fast save with his permission.
The second case: infrequent fast; which occurs once a year such as the fasting on the day of Arafa, Ashura’ and the like. In this case she is permitted to fast without his permission save if he prevented her in the first place. In this regard, it is stated: ”the wife isn’t permitted to perform voluntary fasts that reoccur more than once a year save with the husband’s permission, but as for infrequent fasts such as fasting on the day of Arafa and Ashura’, in this case she is permitted to fast without his permission save if he prevented her from doing so and the same applies on long-term make up.” [Hashyat Al-Byjirmi]
However, if the wife fasted without the husband’s permission then her fast is valid yet she is sinful, but if she had his consent, then it is similar to having his permission without being said as stated in [Hashyat Al-Byjirmi].
Finally we (Iftaa’ Dept) would like to draw your attention that spouses should cooperate and help one another in seeking Allah’s, The Exlated satisfaction without neglecting their duties and rights toward each other. And Allah knows best.