Sahih Muslim Book 10, Hadith Number 3813.
Chapter : Riba (Usury).
Abu Zubair heard Jabir b. ‘Abdullah (Allah be pleased with him) saying: Allah’s Messenger (may peace be upon him) ordered us to kill dogs, and we carried out this order so much so that we also kill the dog coming with a woman from the desert. Then Allah’s Apostle (may peace be upon him) forbade their killing. He (the Holy Prophet further) said: It is your duty the jet-black (dog) having two spots (on the eyes), for it is a devil.