Praise be to Allah.
Fasting Ramadaan is an important obligation which Allaah has enjoined upon His believing slaves in the verse in which He says (interpretation of the meaning):
“O you who believe! Observing As-Sawm (the fasting) is prescribed for you as it was prescribed for those before you, that you may become Al-Muttaqoon (the pious)”
Every adult Muslim who is of sound mind is obliged to fast, unless he has a legitimate shar’i excuse, such as those who are sick or travelling. They are allowed not to fast, but they have to make it up. Women who are menstruating or bleeding following childbirth are also obliged to break the fast and make it up later. If a person breaks the fast in Ramadaan without an excuse, he has committed a major sin, and he has to repent to Allaah, but does he have to make up the day when he broke the fast?
That depends. If he intended to fast and then broke the fast during the day with no excuse, then he has to make it up. If he did not intend to fast at all, then the more correct view is that he does not have to make it up.
Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said: Breaking the fast during the day in Ramadaan with no legitimate excuse is a major sin, and a person is a faasiq (rebellious evildoer) if he does that. He has to repent to Allaah and make up the day when he broke the fast. i.e., if he fasts then during the day he breaks the fast with no legitimate excuse, then he has sinned and he has to make up that day when he broke the fast, because when he started it, it became binding on him so he has to make it up, like a vow. But if he deliberately did not fast from the outset, with no excuse, then the most correct view is that he does not have to make it up, because that will not benefit him in any way. The basic principle is that every act of worship that is to be done at a specific time, if it is delayed beyond that time with no legitimate excuse, it will not be accepted, because the Prophet (peace and blessings of Allaah be upon him) said: “Whoever does an action that is not in accordance with this matter of ours will have it rejected.” And because this is a transgression of the sacred limits set by Allaah, and transgression of the sacred limits of Allaah is wrongdoing, and the deeds of the wrongdoer are not accepted. Allaah says (interpretation of the meaning):
“And whoever transgresses the limits ordained by Allaah, then such are the Zaalimoon (wrongdoers)”
If he had done this act of worship ahead of time, it would not be accepted from him either, and similarly if he does it after its time, it will not be accepted, unless he has an excuse.
End quote from Mamjoo’ Fataawa al-Shaykh Ibn ‘Uthaymeen (19/question no. 45).
If a person breaks the fast in Ramadaan without an excuse, if he breaks it by having intercourse, then as well as making up the fast, he has to offer expiation, which is freeing a slave; if he cannot do that then he must fast for two consecutive months. If he is not able to do that then he has to feed sixty poor persons. No differentiation is made between men and women in this regard, if the woman had intercourse willingly, but if she was forced then she does not have to offer expiation.
If the breaking of the fast did not involve having intercourse, rather it was by eating or drinking etc, then the fuqaha’ differed as to whether the expiation must be offered in that case. The most correct view is that it is not required.
There is no evidence to suggest that the expiation is required of one who breaks the fast, and it is not valid to draw an analogy with intercourse.
Ibn Qudaamah (may Allaah have mercy on him) said: There is no text to suggest that the expiation is required except in the case of intercourse, and it is not valid to draw an analogy with intercourse.
End quote from al-Mughni (3/22).
If a woman is required to fast for two consecutive months, and she starts fasting then her period comes, that does not break the continuity of her fasts. She should stop fasting, then make up the days of her period, then complete the two months, because menstruation is something that Allaah has decreed for the daughters of Adam, and she has no control over it. This is something on which the scholars are agreed.
Ibn Qudaamah (may Allaah have mercy on him) said: The scholars are unanimously agreed that if a woman who is fasting two consecutive months menstruates before she completes the fasts, she should make up those days when her period ends, and complete the number based on the days that she has already fasted. That is because menstruation cannot be avoided during those two months except in the case of a woman who has reached menopause.
End quote from al-Mughni (8/21).
Based on this, if she offers this expiation by fasting in Muharram and Safar, for example, and her period is seven days in each month, then she should stop fasting during the days of her period, and start fasting immediately afterwards, and add on fourteen days of Jumaada al-Oola to make up for the days of her period.
And Allaah knows best.