It is narrated from Sayyiduna Salamah that once the Prophet (peace and blessings be upon him) passed by a house in the courtyard of which a water-skin was hanging. The Prophet (peace and blessings be upon him) asked those people for water to drink. They said, "This is the skin of a dead animal." The Prophet (peace and blessings be upon him) said: "Tanning purifies the skin."