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