(Muslim, Abū Dāwūd, and Ibn Khuzaymah) and he used to say: "A man's prayer is invalidated if there is not in front of him something like the back of a saddle: a woman [who is menstruating], a donkey, and a black dog." Abū Dharr said: I asked, "O Messenger of Allāh, what is the matter with the black dog as opposed to the red one?" He replied, "The black dog is a devil." Prayer facing the grave