How should a woman whose regular menstruation is less than ten days act in fulfilling her religious duties if her…

According to the Hanafi school, the minimum duration of menstruation is three days and the maximum is ten days. Bleeding that lasts less than three days or more than ten days is not considered menstruation but istihada (bleeding due to illness, not related to menstruation or postpartum bleeding). The minimum period of purity between two menstrual cycles is fifteen days. (Mergînânî, el-Hidâye, 1/32; Mevsılî, el-İhtiyâr, 1/26)

If a woman with a regular menstrual cycle continues to bleed after her usual (habitual) menstruation days and this bleeding does not exceed ten days, all of the bleeding is considered menstruation. However, if the bleeding exceeds ten days, all bleeding after her habitual menstruation days is considered istihada. (Serahsî, el-Mebsût, 3/178; Ibn al-Humam, Fath al-Qadir, 1/176-178) For example, if a woman’s regular period is six days and her bleeding continues but does not exceed ten days, all the days with bleeding are counted as menstruation. But if her bleeding exceeds ten days, all bleeding after the sixth day is considered istihada. This woman must perform her prayers and fasts after the tenth day, and she must also make up any prayers and fasts missed between her habitual six days and the tenth day. (Aynî, al-Binaya, 1/664-665; Ibn Nujaym, al-Bahr, 1/223)

Although these are the basic rulings, in rare cases, some women may regularly bleed for less than three days or more than ten days. Accordingly, women who regularly experience bleeding for less than three days or more than ten days may, if supported by medical examination, consider bleeding lasting less than three days or up to fifteen days as menstruation.

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu