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“In the name of Allah the Most Gracious, the Most Merciful.”
Ruling No 1: If a woman stopped bleeding at night, in Ramadhan, at the maximum ten days (240 hours), she will have to fast that day, even if she stopped menstruating just a minute before dawn. This is because her bleeding has reached the maximum days / time of haydh. If she delays her ghusl until after Fajr, she will be required to make up any prayers she missed during that time (Isha/fajr).
Ruling No 2: If a woman stops bleeding in Ramadhaan, during the day, it will not be proper for her to eat or drink for the rest of the day. It is necessary for her to behave like a fasting person until sunset, even though it will not be considered a fast for her, and she will have to make up for it later. Whereas on the day her menstruation begins, it is permissible for her to eat and drink on that day and on all the days she is not fasting.
Ruling No 3: If a woman stopped bleeding at night in Ramadhan BEFORE the maximum ten days (240 hours) and she had time in which she could at least take a ghusl (10-15 mins) and say the takbeer (Allahu Akbar) of salaah, then she will have to fast that day. If she had time but delays her ghusl until after Fajr (before mid-morning), she will be required to make up any prayers she missed during that time (Isha/fajr).
If she ends her menstruation with less time than this, she will not fast that day, but will have to abstain from eating & drinking until after sunset. She will be obligated to make up the fast after Ramadhan.
Ruling No 4: A woman has to be completely sure that she has finished her menstruation before she intends to keep a fast, before subah sadiq (fajr beginning time). If she feels like she may become pure in a few hours after suhoor, it will not be permissible for her to fast.
The latest a woman can delay her intention is until the Islamic midday for her fast to be valid. However, one will be sinful for delaying ghusl and missing fajr salaah.
Note: The Islamic midday is the half-way point between dawn (Fajr beginning time) and sunset.
A woman should not purposefully delay ghusl as this may result in missing salaah in its due time.
Ruling No 5: If a woman begins to bleed while fasting, even if it may be a few minutes before sunset, her fast will break and she will have to make qadha of it.