It was narrated from Ibn Wa'lah 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 Wa'lah said: "Is this your own opinion, or something that you heard from the Messenger of Allah?" He said: "No, (I heard it) from the Messneger of Allah

English translation · Sunan an-Nasa'i