It is narrated from Mu'tamir (bin Sulaiman) that his father asked Qatadah: A woman who knows the days of her menstruation, and if blood continues to flow for five, four, or three more days, what should she do? He replied: She should perform prayers. Sulaiman said: If the blood continues for two days? He replied: This is still menstrual blood. He said: And I asked Imam Ibn Sirin, may Allah have mercy on him, and he said: Women know this matter better.
Hadith Takhrijاس قول کی سند صحیح ہے۔ دیکھئے: [مصنف ابن أبى شيبه 538/2، 8864] ، [أبوداؤد 286] ، [المحلي 203/2] و [التمهيد 75/16]
Brief Explanation
(Commentary on Hadiths 800 to 818)
The purpose is that there is a difference between the blood of menstruation (hayd) and the blood of irregular bleeding (istihada), and a woman can distinguish between them as to when the menstrual blood has ended. Therefore, when there is menstrual blood, she should leave the prayer; otherwise, after performing ritual bath (ghusl) and ablution (wudu), she should offer the prayer.
It should be clear that the days of menstruation (hayd) sometimes increase or decrease, so if one or two days are added and the blood is still menstrual blood, then the rulings of menstruation will apply to it.