Sahih Bukhari 3323

Narrated 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. ..

Narrated Sufyan bin Abi Zuhair Ash-Shani: That he heard Allah's Apostle saying, If somebody keeps a dog that is neither used for farm work nor for guarding the livestock, he will lose one Qirat (of the reward) of his good deeds everyday. ..