What is the ruling on a wife fasting a supererogatory fast without her husband's knowledge, given that he knows she is fasting a supererogatory fast, and does his knowledge of her fasting negate the reason for not seeking his permission?

A woman is not permitted to observe a voluntary fast while her husband is present unless she has his permission. The reason for this is that her fasting would deprive him of his right to enjoy her. Two situations are exempted from this rule:

1. If the husband is absent, because he cannot enjoy her at that time.

2. If the husband is unable to enjoy her due to illness, or if he himself is fasting, then the wife may observe a voluntary fast without his permission, as there is no need (for his permission) in these cases.