Abu Dawud Book 1, Hadith Number 293.
Chapter : A person who is sexually defiled is permitted to eat anything before washing.
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.