he is away, she is free to fast. Yet if he is present she must not fast, because he may summon her to satisfy his desire while she is fasting, placing both of them in difficulty.
As for an obligatory fast—such as when she still owes days from Ramadan and only the same number of days remain before the next Ramadan—she is required to fast whether he gives permission or not. For example, if a woman has ten days to make up from Ramadan and only ten days remain before the next Ramadan, she must fast them regardless of his consent; indeed, even if he forbids her she may still fast, for it is a binding duty.
However, if she owes ten days from Ramadan and there is still a month, two months, or more before the coming Ramadan, he may prevent her from fasting and it is not lawful for her to fast without his leave, because the time is ample and she should not impose hardship on her husband. If he later consents and she begins the fast, then—provided it is obligatory—it is forbidden for him to invalidate it through intercourse, for he has approved it and she has embarked upon an act she is bound to complete. If the fast is voluntary, he may have intercourse with her even though that breaks the fast, for a voluntary act does not have to be finished. Yet should she say, “You have granted me permission and promised not to break my fast,” he must honour that pledge and is forbidden to spoil her fast, in keeping with Allah’s words: “And fulfil the covenant; indeed, the covenant will be questioned about” (Q 17:34).
Regarding the Prophet’s statement that she “must not admit anyone into his house except with his permission,” it means she should not allow anyone to enter without his consent. If he expressly forbids a particular person—saying, for instance, “So-and-so is not to enter my house”—then it is unlawful for her to let that individual in, for the house belongs to him. But if the husband is broad-minded and unconcerned about who visits his family, she is not obliged to seek his permission for every visitor.
Allah is the One who grants success.