It is narrated from Sayyiduna Salamah bin al-Muhabbiq (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him), during the expedition of Tabuk, came to a house, and there was a waterskin hanging there. He (peace and blessings be upon him) asked for water, and the Companions (may Allah be pleased with them) said: It is (made from the skin of) a carcass. So he (peace and blessings be upon him) said: "Its tanning is its purification."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 52