Musannaf Ibn Abi Shayba 16:552

Abu Bakr narrated to us, he said: Abu Khalid—and he is not al-Ahmar—narrated to us, from Hisham, from Qatadah, from al-Hasan, from Jun ibn Qatadah, from Salamah ibn al-Muhabbaq, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The purification of hides is their tanning."