Abu Dawud Book 1, Hadith Number 286.

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

Narated By Fatimah daughter of Abu Hubaysh : Urwah ibn az-Zubayr reported from Fatimah daughter of Abu Hubaysh that her blood kept flowing, so the Prophet (PBUH) said to her: When the blood of the menses comes, it is black blood which can be recognised; so when that comes, refrain from prayer; but when a different type of blood comes, perform ablution and pray, for it is (due only to) a vein.