It was narrated that Ibn 'Abbas (رضي الله عنه) said:

The Messenger of Allah (ﷺ) passed by a dead sheep and said: "Why don't you make use of its skin?” They said: O Messenger of Allah, it is maitah [i.e., it died of natural causes and i was not slaughtered properly]. He said: "It is only hartm to eat it."