Hides of dead animals are purified by tanning
وَحَدَّثَنَا ابْنُ أَبِي عُمَرَ، وَعَبْدُ اللَّهِ بْنُ مُحَمَّدٍ الزُّهْرِيُّ، - وَاللَّفْظُ لاِبْنِ أَبِي عُمَرَ - قَالاَ حَدَّثَنَا سُفْيَانُ، عَنْ عَمْرٍو، عَنْ عَطَاءٍ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم مَرَّ بِشَاةٍ مَطْرُوحَةٍ أُعْطِيَتْهَا مَوْلاَةٌ لِمَيْمُونَةَ مِنَ الصَّدَقَةِ فَقَالَ النَّبِيُّ صلى الله عليه وسلم " أَلاَّ أَخَذُوا إِهَابَهَا فَدَبَغُوهُ فَانْتَفَعُوا بِهِ " .
Ibn Abbas reported: The Messenger of Allah (ﷺ) happened to pass by a goat thrown (away) which had been in fact given to the freed slave-girl of Maimuna as charity. Upon this the Messenger of Allah (way peace he upon him) said: Why did they not get its skin? They had better tan it and make use of it.