Musnad Ahmad 937:90

Bahz narrated to us, Sulayman ibn al-Mughirah narrated to us, Humayd narrated to us, from Abdullah ibn al-Samit, from Abu Dharr, who said: The prayer of a man is severed if there is not in front of him something like the back of a saddle: a woman, a donkey, and a black dog. I said to Abu Dharr: What is the matter with the black dog as opposed to the red dog? He said: O son of my brother, I asked the Messenger of Allah, peace and blessings of Allah be upon him, just as you asked me, and he said: "The black dog is a devil."