Abu Dawud Book 1, Hadith Number 284.
Chapter : A person who is sexually defiled is permitted to eat anything before washing.
Narated By ‘Aisha, Ummul Mu’minin : Bahiyyah said: I heard a woman asking ‘Aisha about the woman whose menses became abnormal and she had an issue of blood. The Apostle of Allah (PBUH) asked me to advise her that she should consider the period during which she used to menstruate every month, when her menstruation was normal. Then she should count the days equal to the length of time (of her normal menses); then she should abandon prayer during those days or equal to that period. She should then take a bath, tie a cloth on her private parts a pray.