All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
The view of the majority of the scholars is that the maximum period of menses is 15 days. Therefore, the blood discharges after this period are considered as Istihaadhah (bleeding outside the monthly menses), and a woman during Istihaadhah should not give up performing prayers and fasting.
The conclusion that may be deducted from all the Prophetic narrations that are mentioned regarding a woman who has discharges outside her monthly periods is that her situation is one of the following three cases:
1. The woman has a known period of menses, so she acts according to it and refrains from praying and fasting, etc, and at the end of her menses, she performs Ghusl (i.e. a ritual bath) and performs the prayer and fasts.
2. She distinguishes between the blood of menses and the blood of Istihaadhah by its colour or smell . In which case, she acts according to the type of the blood she observes.
3. She does not have monthly periods at all, or that she had once but she forgot, and she is not able to distinguish whether the blood is that of menses or Istihaadhah. In this case, she should act according to the menstruation period of most women, which is six to seven days.
Therefore, the ruling on a woman who has bleeding for one month or nearly so becomes clear to you.
As regards the second case when the duration of her monthly menses is less than the usual period of time, or that her monthly menses comes little by little; in this case, she should perform Ghusl (i.e. a ritual bath) and offer prayers and fast whenever she recognizes purity, even if her usual days of menses were not complete.
Allaah Knows best.