Abu Dawud Book 1, Hadith Number 361.

Chapter : A peerson who is sexually defiled is permitted to eat anything before washing.

Narated By Asma, daughter of Abu Bakr : A woman asked the Apostle of Allah (PBUH): Apostle of Allah, what do you think if the clothe of any of us is smeared with the blood of menstruation; what should she do? He said: If (the clothe of) any of you is smeared with the blood of menstruation, she should scratch it; then she should sprinkle water upon it and then she may pray.