Musannaf Ibn Abi Shayba 16:606

Abu Bakr narrated to us, he said: Abd al-Wahhab narrated to us, from Ayyub, from Muhammad, from Usayd ibn Jabir, that he used to dislike khuffs (leather socks) and sandals that were not slaughtered (i.e., made from the hide of an animal that was not slaughtered according to Islamic law).