"The Messenger of Allah said: 'Whoever keeps a dog which he does not need for farming or livestock, one Qirt will be deducted from his (good) deeds each day.' It was said to him: 'did you hear this from the Messenger of Allah He said: 'Yes, by the Lord of this Masjid."'
Sunan an-Nasa'i Book 42, Hadith 23