The Messenger of Allah (peace be upon him) knew that the temperaments of women in this matter are different; a woman might menstruate for three days, and it might be five, six, seven, or more or less than that. Thus, he left whatever duration that was as the time of her menstrual cycle (iqra'); that matter was left to her. The Prophet (peace be upon him) ordered one of the women who asked him: 'Sit for the days of your menstrual cycles.' He ordered another: 'When menstruation begins, cease praying, and when it ceases, pray.' He ordered Hamna bint Jahsh, when she complained excessively to him about the confusion of her menstruation, saying: 'I have a massive flow,' and he commanded her at that time to exercise discretion (taharri), saying: 'Menstruate for six or seven days in the knowledge of Allah, then pray for twenty-three or twenty-four nights and their days.' He thereby established her time—when her menstruation became confused—as a menstruation and a period of purity each month; this is according to the meaning of the cycles (al-iqra'), for he established a menstrual period for every month in the 'idda. This is how the majority of women's menstruation is, although the Prophet (peace be upon him) spared women the burden of counting, saying: 'Six or seven days, just as women menstruate and just as they become pure according to the timing of their menstruation and their purity.'

Abu Ya'qub said: 'The ruling for istihada is what the Prophet (peace be upon him) established for the women who experienced it and asked him. He commanded each one of them according to her condition with a different ruling, and he referred each one of them back to her own nature. He did not make the ruling for every woman who experiences istihada the same as the ruling for all the women of the world. He said to some of them: [Observe] the days of her menstrual cycles if she knows them; whether ten, fifteen, or less or more, provided those were known cycles during the month. He said to another: "When the menstruation begins, cease praying." And he said to the third, whose menstruation became confused with her istihada: [Observe] a menstrual period and a period of purity during the month—which is what we have described from the words of the Prophet (peace be upon him) to Hamna bint Jahsh at the beginning of the chapter on menstruation. Thus, a woman will hardly exceed in her blood what we have described.'