A'isha (Radiya Allahu Anha) reported that Jibreel (peace be upon him) made a promise with Allah's Messenger (salla allahu alayhi wasallam ) to come at a definite hour; that hour came, but Jibreel did not visit him. And there was in his hand (in the hand of Allah's Messenger) a staff. He threw it from his hand and said: Never has Allah or His messengers (angels) ever broken their promise. Then he cast a glance (and by chance) found a puppy under his cot and said: 'A'isha, when did this dog enter here? She said: BY Allah, I don't know.
He then commanded and it was turned out. Then Jibreel came and Allah's Messenger (may peace be upon him) said to him: You promised me and I waited for you, but you did not come, whereupon he said: It was the dog in your house which prevented me (from coming), for we (angels) do not enter a house in which there is a dog or a picture.



[Sahih Muslim : Book 24, Number 5249]

Lesson learned: keep the dog outside, and do not hang the picture in your house.