From Sahih Bukhari (Hadith 4932):
Narrated Ibn `Abbas:(as regards the explanation of Hadith 454). 'Indeed, it (Hell) throws about sparks (huge) as Forts.' We used to collect wood in the form of logs, three cubits long or shorter. for heating purposes in winter., and we used to call such wood, the Qasr
Reference: Bukhari 4932