Purification (Kitab Al-Taharah)

Dawud :: Book 1 : Hadith 286

Narrated Fatimah daughter of AbuHubaysh:

Urwah ibn az-Zubayr reported from Fatimah daughter of AbuHubaysh that her blood kept flowing, so the Prophet (peace_be_upon_him) 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.