Where the right of Allah is concerned, the rights of individuals do not take precedence. Accordingly, although spouses have certain rights over one another, these rights do not in any way prevent the performance of obligatory acts of worship. Therefore, even if a husband does not grant permission, a woman fulfills her obligatory acts of worship such as prayer, fasting, and pilgrimage.
However, if a woman wishes to observe a voluntary (nafl) fast, she should seek her husband’s permission, since in such a case he may have a legitimate need for her. If she begins a voluntary fast without his permission, the husband is entitled to ask her to break the fast. If the fast is broken, she later makes it up (qaḍāʾ) either with his permission or at a time when he is not present.
The Messenger of Allah ﷺ said:
“It is not lawful for a woman to observe a voluntary fast while her husband is present except with his permission.”
(Muslim, Zakāh, 107)
It is evident that this ruling contains multiple wisdoms aimed at preserving harmony and balance within marital life.