Is it permissible for a wife to fast supererogatory fasts (such as Mondays and Thursdays) without her husband's knowledge, and is it permissible for her to seek a general permission from him for fasting? And is it permissible for her to perform supererogatory prayers if her husband dislikes that, for example, if he is in a hurry to go out?

It is not permissible for a woman to observe a voluntary fast while her husband is present except with his permission; this is out of respect for his right and a concern for the stability of marital life. He is allowed to break her fast through intercourse if she fasted without his permission. Likewise, she is not allowed to offer voluntary prayers or other supererogatory acts when her husband needs her, and he may interrupt her supererogatory prayer if he calls her to his bed. This is because the husband's right is an obligation that takes precedence over supererogatory acts. The husband should help his wife in obeying Allah, due to the immense reward therein. He is not permitted to mock her worship or restrict her.