Sahih Bukhari
Sahih Bukhari Volume 001, Book 004, Hadith Number 173.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 04. Ablutions (Wudu')
Narated By Abu Huraira : Allah's Apostle said, "If a dog drinks from the utensil of anyone of you it is essential to wash it seven times."