I heard the Messenger of Allah ﷺ say, "When a hide is tanned, it has been purified."
حدثنا محمد بن كثير أخبرنا سفيان عن زيد بن أسلم عن عبد الرحمن بن وعلة
سمعت رسول الله ﷺ يقول إذا دبغ الإهاب فقد طهر
Muslim narrated it in Kitab al-Hayd, chapter on the purification of the skins of dead animals through tanning, hadith no. 366, from the hadith of Sufyan, through him.