What is the basis for establishing the menses duration for a woman whose bleeding is continuous and undifferentiated (Istihadah) when the typical duration is six or seven days?
Chapter on Menstruation
Al-Mughni
Book of Purification
Primary text
The ruling is to establish her menses as six or seven days because this is the typical duration for most women, and her condition is assumed to resemble that of the majority of women, requiring her to be reverted to this standard, just as her timing is reverted to one menses per month. This is one position held by Al-Shafi'i. Evidence for this is found in the Hadith of Humnah, where the Prophet, peace be upon him, reverted her duration to six or seven days, not reverting her to the minimum certainty, the custom of her relatives, or the maximum duration of menses.
Supporting text
Another opinion from Ahmad states she sits for one day and one night each month, which is the second position of Al-Shafi'i, based on the certainty (day/night) while the excess is doubtful and should not override certainty. A third narration holds that she sits for the maximum duration of menses, which is the madhhab of Abu Hanifa, considering the entire period as potential menses time. A fourth opinion states she observes the custom of her female relatives, supported by 'Ata', Al-Thawri, and Al-Awza'i.