258. Abu Dhar narrated that the Messenger of Allah salla alayhi wa sallam said: ´´When one of you stands for prayer, there should be a thing before him like the back of the saddle, and in case there is nothing in front of him (a thing) like the back of the saddle, his prayer would be nullified by (passing of an) ass, a women, or a black dog.´´ I (the narrator) said: ´´O Abu Dhar, what is the difference between a black dog and a white dog or the yellow dog?´´ He said: ´´O son of my brother, I asked the Messenger of Allah salla alayhi wa sallam as you have asked me, and he said: ´´The black dog is a Satan (devil).´´