Sunan An-Nasai, Chapter: The Book of Purification

"Fatimah bint Abu 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 it is not menstruation. When your period comes, stop praying, and when it goes wash the traces of blood from yourself and perform Wudu. That is a vein and is not menstruation.'" It was said to him: "What about Ghusl?' He (saw) said: "No one doubts that." Abu Abdur-Rahman said: "I do not know anyone who mentioned 'and perform Wudu in this Hadith except Hammad bin Zaid, for some others have reported it from Hisham, and they did not mention 'and perform Wudu in it." (Sahih)