Musnad Ahmad 1153:1041

Waki' narrated to us, al-A'mash narrated to us, from Habib, from 'Urwah, from 'Aishah, from the Prophet (peace and blessings of Allah be upon him), who said: "The woman suffering from prolonged non-menstrual bleeding (mustahadah) shall pray, even if the blood drips onto the mat."