It is narrated from Sayyidah Aishah (may Allah be pleased with her) that the sister of Sayyidah Zaynab bint Jahsh (may Allah be pleased with her) had istihadah for seven years. She would fill her tub with water, then enter it (to bathe), and the redness of the blood would rise above the water. She asked the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) said: "This is not menstruation; rather, it is a vein. Perform ghusl and pray." (b) This narration does not contain the order to perform ghusl for every prayer; this is in agreement with all the narrations of Imam al-Zuhri.
The narration of Muhammad bin Ishaq from al-Zuhri is an error, because it contradicts all the other narrations from al-Zuhri and contradicts the authentic narration of Irak bin Malik, from Urwah, from Aishah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحيض / 1642