Sahih Bukhari, Hadith: Q2223, (103) Chapter. The fat of the dead animal should not be melted, nor should it be sold.

صحيح البخاري

Sahih Bukhari

كتاب البيوع

The Book of Sales (Bargains)

باب لا يذاب شحم الميتة ولا يباع ودكه:

(103) Chapter. The fat of the dead animal should not be melted, nor should it be sold.