And the explanation of the evidence that the tanning by polytheists purifies the hides.

Sayyiduna Imran bin Husayn (may Allah be pleased with him) narrates that once we were on a journey with the Messenger of Allah (peace and blessings be upon him). The Prophet (peace be upon him) called a certain person and Sayyiduna Ali bin Abu Talib (may Allah be pleased with him) and said: "Go and search for water for us." So both of them went in search of water. They met a woman who was riding a camel between two water skins or two water bags. They asked her, "Where is water?" She replied, "Yesterday at this time I was at the water spring, and our men are behind." Sayyiduna Ali (may Allah be pleased with him) said to her, "Come with us." She asked, "Where?" They said, "To the Messenger of Allah (peace and blessings be upon him)." She said, "Is he the same person who is called a Sabi (one who has left the religion)?" They replied, "Yes, he is the one whom you think." So both of them took her and brought her to the Messenger of Allah (peace and blessings be upon him), and informed him of the whole situation. The Prophet (peace and blessings be upon him) said: "Tell her to dismount from her camel." Then the Messenger of Allah (peace and blessings be upon him) asked for a vessel, and placed the mouths of the bags or water skins into it. They said that then the Prophet (peace and blessings be upon him) rinsed his mouth and poured the water back into the bags or water skins. Then their mouths were opened and it was announced among the people that they should drink themselves and give their animals to drink. The narrator narrated the complete long hadith.