Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 293
Narated By Zaynab daughter of Abu Salamah : Abu Salamah said: Zaynab daughter of AbuSalamah reported to me that a woman had a copious flow of blood. She was the wife of Abdur Rahman ibn Awf. The Apostle of Allah (pbuh) commanded her to take a bath at the time of every prayer, and then to pray. He reported to me that Umm Bakr told him that 'Aisha said: The Apostle of Allah (pbuh) said about a woman who was doubtful of her menstruation after purification that it was a vein or veins.