Abu Dawud

Benefits and Issues:
➊ During fasting, conjugal relations between spouses cannot take place.
➋ Furthermore, due to hunger and thirst, a certain heaviness or irritability naturally arises in one’s disposition, and it is only natural that husbands generally do not tolerate such a state, and its consequences can be inappropriate.
➌ Therefore, the Shari‘ah has not permitted even the slightest disruption in their relations, and has made it obligatory upon the wife to obtain her husband’s permission for voluntary (nafl) fasting.
➍ It is also understood from this that the wife should be extremely sensitive and responsible regarding her husband’s satisfaction; these matters are not merely psychological, but are also prescribed by the Shari‘ah.

Hadith Commentary:
It is also prohibited for a non-mahram man to enter the husband’s house without permission.
The meaning is that a woman should not spend from the wealth that her husband has given her—such as her monthly allowance—without her husband’s permission. As is mentioned in the narration of Abu Dawud, a woman cannot give her husband’s wealth in charity, except from her own food, and in that case, both will receive equal reward.
The spending referred to here is also that which is customary and would not anger the husband upon hearing of it.

Hadith Commentary:
Allowing someone to enter the house without the husband's permission poses the risk of creating suspicion in his heart, which can poison the marital life in the future. However, necessities are exempted from this prohibition, for example:
If someone has a right to enter that house, or if it is a place specifically designated for guests.
(Fath al-Bari: 9/369)
Some people have also exempted the woman's father from this ruling, but according to our inclination, he too is included in this prohibitive command.
And Allah knows best.

Hadith Commentary:

A voluntary fast is a supererogatory act of worship, whereas obedience to the husband is obligatory for the woman. Therefore, the fulfillment of an obligation takes precedence over a supererogatory act of worship. If a man desires intimacy with his wife during the day, the woman must break her voluntary fast. Thus, it is better for her to seek permission beforehand if she wishes to observe a voluntary fast.

Hadith Commentary:
Obedience to the husband is obligatory, and a voluntary fast (nafl) is an additional act of worship; therefore, under no circumstances can a voluntary act be given preference over an obligation. However, if the husband is on a journey, then the woman may observe a fast without his permission, because at that time the husband cannot require any service from her.

Hadith Commentary: Benefits and Issues: (1)
A woman may spend from the household’s commonly used items in small amounts according to social custom, and wealth spent with this customary permission—even without the husband’s knowledge—will also be a source of reward for the husband, because it is from his earnings. The woman, due to her act of spending, will also share in the reward, but each will have their own independent reward. The meaning of “half and half” is not that there is a single reward which is divided between the two.

(2)
It is not permissible for a stranger or non-mahram to come and go in someone’s house. However, with the husband’s permission, a mahram or non-mahram relative may come in his presence, and even in his absence, with his permission, provided that such visits do not lead to any harm. Similarly, a woman may not observe voluntary fasts (other than Ramadan) in the presence of her husband without his permission, so that mutual harmony in marital relations is not disturbed.

English Commentary:
1: ((Lā taṣūmu)) is a negative form which conveys the meaning of prohibition.
In the narration of Muslim, the words ((Lā yaḥillu lil-mar’ati an taṣūma)) are mentioned.
This hadith indicates that in the presence of her husband, it is not permissible for a woman to observe voluntary fasts without her husband's permission.
And this prohibition is absolute; it includes the fasts of the Day of ‘Arafah and ‘Ashura as well. Some people have made an exception for the fasts of ‘Arafah and ‘Ashura.