Musnad Ahmad 30:2366

Isma'il narrated to us, he said: Hisham al-Dastawa'i informed us, he said: Yahya ibn Abi Kathir narrated to us, from Abu Salamah, from Abu Hurayrah, he said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "Whoever keeps a dog, his deeds will decrease by one qirat every day, except for a dog for tillage or livestock."