Musnad Ahmad 27:32

Isma'il narrated to us, Ayyub narrated to us, from Nafi', from Ibn 'Umar, from the Prophet (peace be upon him) that he said: "Whoever takes—or he said: acquires—a dog that is not a hunting dog, nor a livestock dog, two qirats of his reward decrease every day." It was said to him: "Indeed, Abu Hurayrah says: 'Or a farm dog?'" He replied: "How would Abu Hurayrah have a farm?"