(a) Abd al-Rahman bin Mahdi (may Allah have mercy on him) said that a woman called Umm al-Ala' said: My menstruation, for all time, has been two days. (b) Ishaq said: It is soundly established for us in our time from more than one woman that she said: My menstruation is two days. (c) Yazid bin Harun (may Allah have mercy on him) said: I have a woman (in my household) who menstruates for two days. (d) It is narrated from Imam al-Shafi'i (may Allah have mercy on him) that he said: "I saw a woman who never menstruated more than one day, and this remained her habit always; and (I knew of) several women who menstruated for less than three days, some women for fifteen days, and one woman who menstruated for thirteen days." (e) The Shaykh (may Allah have mercy on him) said: It is reported from Sayyiduna Ali (may Allah be pleased with him) and Shurayh (may Allah have mercy on him) that they both allowed three menstrual periods within one month and five nights; its discussion will come in Kitab al-Idad (the Book of Waiting Periods). (f) Imam al-Shafi'i (may Allah have mercy on him) said: We regard the narration of Sayyiduna Ali (may Allah be pleased with him) as agreeing with the narration of the Prophet (peace and blessings be upon him), in that he did not fix (a duration for) menstruation. His evidence is this hadith of the Prophet (peace and blessings be upon him): "When your menstruation comes, leave the prayer, and when its duration has passed, wash the blood off your body and pray."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحيض / 1534
It is narrated from Sayyidah Aishah (may Allah be pleased with her) that Fatimah bint Abi Hubaysh (may Allah be pleased with her) said to the Messenger of Allah (peace and blessings be upon him): "O Messenger of Allah, I do not become pure; shall I leave the prayer?" The Messenger of Allah (peace and blessings be upon him) said: "That is from a vein; it is not menstruation. When menstruation comes, leave the prayer, and when its duration has passed, wash the blood off yourself and pray."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحيض / 1535