It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever keeps a dog that is neither for guarding fields or sheep nor a hunting dog, then his reward will decrease by one qirat every day."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 5505