It is narrated from Sayyiduna Jabir (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) commanded us to kill dogs, so much so that if a woman brought her dog from the village, we would also kill it. Later, the Prophet (peace and blessings be upon him) forbade this: Only kill the black dog with two spots, for it is a devil.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 14575