Sahih Muslim, Chapter: The Book of Menstruation (Kitab Al-Haid)

Fatimah b. Abu Hubaish came to the Apostle (may peace be upon him) and said: I am a woman whose blood keeps flowing (even after the menstruation period). I am never purified; should I, therefore, abandon prayer? He (the Holy Prophet) said: Not at all, for that is only a vein, and is not a menstruation, so when menstruation comes, abandon prayer, and when it ends wash the blood from yourself and then pray.