Musnad Ahmad 30:503

'Abd al-Razzaq narrated to us, from Ma'mar, from al-Zuhri, from Abu Salamah, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: "Whoever keeps a dog, except for a hunting dog, or a dog for crops, or for livestock, a qirat of his reward decreases every day."