Musnad Ahmad 5:47

Abu Bakr ibn Ayyash narrated to us, Mughirah ibn Miqsam narrated to us, al-Harith al-Ukli narrated to me, from Abdullah ibn Naji, who said: Ali said: I had two times of entry to the Messenger of Allah, may Allah bless him and grant him peace, by night and by day. Whenever I entered upon him while he was praying, he would clear his throat. I came to him one night, and he said: "Do you know what the Angel brought about tonight? I was praying, and I heard a rustling in the house. I went out, and there was Gabriel, peace be upon him. He said: 'I have been waiting for you all night. There is a dog in your house, so I could not enter. We do not enter a house in which there is a dog, nor a person in a state of major ritual impurity (junub), nor an image.'"