Sayyiduna Ibn Umar (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever keeps a dog, other than a hunting dog or a dog for guarding livestock, one qirat is deducted from his deeds, and one qirat is equal to the mountain of Uhud."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13149