Sahih Al Bukhari – Book of Beginning Of Creation
Volumn 004, Book 054, Hadith Number 541.
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Narated By Abu Huraira : Allah's Apostle said, "If somebody keeps a dog, he loses one Qirat (of the reward) of his good deeds everyday, except if he keeps it for the purpose of agriculture or for the protection of livestock."
Junaid Tahir