It was narrated from Ibn Walah that he asked Ibn Abbas: "We are attacking the Maghrib, and they are people who worship idols, and they have waterskins in which they keep milk and water." Ibn Abbas said: "Tanning is purification." Ibn Walah said: "Is this your own opinion, or something that you heard from the Messenger of Allah ﷺ?" He said: "No, (I heard it) from the Messneger of Allah صلى الله عليه وسلم.