Sunan An-Nasai, Chapter: The Book of Menstruation and Istihadah

"Fatimah bint Abi Hubaish suffered from Istihadah and she asked the Prophet (saw): 'O Messenger of Allah, I suffer from Istihadah and I do not become pure; should I stop praying?' The Messenger of Allah (saw) said: 'That is a vein and is not menstruation. When your period comes, stop praying, and when it goes wash the traces of blood from yourself and do Wudu'. That is a vein and is not menstruation.'" It was said to him (one of the narrators): "What about Ghusl?" He said: "No one is in doubt about that." (Sahih)