Ibn Wa'lah narrates that he asked Sayyiduna Ibn Abbas (may Allah be pleased with them both): We go on campaigns in this land of the West; they are idol-worshippers and they have waterskins in which milk and water are kept. Ibn Abbas (may Allah be pleased with them both) said: "Tanning (dibagh) purifies." Ibn Wa'lah asked: Is this your own opinion or something you heard? He said: "Rather, it is something I heard from the Messenger of Allah (peace and blessings be upon him)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12923