Purification (Kitab Al-Taharah)
Dawud :: Book 1 : Hadith 67
Narrated AbuSa'id al-Khudri:
I heard that the people asked the Prophet of Allah (peace_be_upon_him): Water is brought for you from the well of Buda'ah. It is a well in which dead dogs, menstrual clothes and excrement of people are thrown. The Messenger of Allah (peace_be_upon_him) replied: Verily water is pure and is not defiled by anything.