Volume 7 · Book 67 · Hadith 390
Narrated 'Abdullah bin Umar: I heard the Prophet saying, "If someone keeps a dog neither for hunting, nor for guarding livestock, the reward (for his good deeds) will be reduced by two Qirats per day."
— Sahih Bukhari, Volume 7, Book 67: Hunting, Slaughtering, Hadith #390