Sahih Muslim Book 003, Hadith Number 0654.
Chapter : The woman who has a prolonged flow of blood, her bathing and prayer.
'Aisha reported: Umm Habiba b. Jahsh thus asked for a verdict from the Messenger of Allah (may peace be upon him): I am a woman whose blood keeps flowing (after the menstrual period). He (the Holy Prophet) said: That is only a vein, so take a bath and offer prayer; and she took a bath at the time of every prayer. Laith b. Sa'd said: Ibn Shihab made no mention that the Messenger of Allah (may peace be upon him) had ordered her to take a bath at the time of every prayer, but she did it of her own accord. And in the tradition transmitted by Ibn Rumh there is no mention of Umm Habiba (and there is mention of the daughter of Jahsh only.)