Al-Istihādah is bleeding that comes from the lower part of the womb, outside of the normal menstrual cycle, due to bleeding from a blood vessel. This is understood from the saying of the Prophet (ﷺ) to Fātimah bint Abee Hubaysh (may Allah be pleased with her):
إِنَّمَا ذَلِكِ عِرْقٌ، وَلَيْسَ بِحَيْضٍ
“It is from a blood vessel, and not due to menses.” (Bukhāri, 228, Muslim, 333)
Ibn Rushd (may Allah have mercy on him) stated: “There is general agreement that if there is extended bleeding ―more than once and more than the menstrual bleeding ―then it takes the ruling of Istihādah (abnormal bleeding). This is based on the saying of the Prophet (ﷺ) to Fātimah bint Abee Hubaysh who suffered from abnormal bleeding:
فَإِذَا أَقْبَلَتْ حَيْضَتُكِ فَدَعِي الصَّلاَةَ، وَإِذَا أَدْبَرَتْ فَاغْسِلِي عَنْكِ الدَّمَ ثُمَّ صَلِّ
“So when your real menses starts, give up your Prayers and when it has finished, wash off the blood and take a bath, and offer your prayers.”
And he (ﷺ) said to her:
ثُمَّ تَوَضَّئِي لِكُلِّ صَلاَةٍ، حَتَّى يَجِيءَ ذَلِكَ الْوَقْتُ
“And perform ablution for every prayer until the time of the next period comes.” (Bukhāri, 228)
The bleeding woman, therefore, should clean her private area of blood, then apply a cotton pad or something similar due to the saying of the Messenger (ﷺ):
أَنْعَتُ لَكِ الْكُرْسُفَ فَإِنَّهُ يُذْهِبُ الدَّمَ
“You should use cotton, for it absorbs the blood.” She said: “There is too much blood for that.” He (ﷺ) said: “Then use a cloth.” (Abu Dawood, 287)
The women who bleed abnormally are of three types:
ONE: The woman who initially starts bleeding, then she should stop praying, fasting and refrain from full sexual relations while she’s bleeding until she becomes pure so long as it does not exceed 15 days from when the bleeding began (so, this type of bleeding is considered as menstrual). This is the position of the majority of scholars.
TWO: If her bleeding continues beyond 15 days, then it is now considered as abnormal (istihādah). In this case, she considers 6 or 7 days among her bleeding days as menstrual bleeding if she cannot distinguish between her menstrual blood and the abnormal blood. The exact number of days she takes as menstruation will be based on following the cycle of women around her, her relatives or her household who bleed normally.
However, if she can tell the difference between her menstrual blood and abnormal blood, then she withholds from prayer, etc, while her menstrual blood is showing ―and menstrual blood is (normally) distinguishable due to its very dark colour and foul odour. So, after the menstrual blood stops, she takes a bath (ghusl) and prays, fasts and can have full sexual relations, even if she still experiences the abnormal type of blood (istihādah which is redder in colour, like a cut blood vessel). But, this is with the condition that her menstrual bleeding does not extend beyond 15 days. That is because a menstrual cycle should not extend beyond 15 days regardless.
THREE: The woman who bleeds constantly, but she knows the length of her menstrual cycle (due to her past periods). So, she stops praying, etc, during this time, then she takes a bath for the end of her menstruation, then she performs ablution (wudoo) before each prayer after the prayer-time begins. And she is allowed to have full sexual relations with her husband until she knows her next cycle should begin.
This is what can be summarised from the ahādeeth of the Prophet (ﷺ) regarding the women who suffer from abnormal bleeding which has been collected in Bulūgh Al-Marām of Al-Hāfidh Ibn Hajr (may Allah have mercy on him), and in Al-Muntaqā of Al-Majd Ibn Taymiyyah (may Allah’s mercy be upon him).
See Al-Jāmi’ fī Fiqhil-‘Allāmah Ibn Bāz (pp. 99-101).