Sahih al-Bukhari 4932
Sahih al-Bukhari · Book 65: Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh)) · The Statement of Allah ta'ala: "Verily! It (Hell) throws sparks (huge) as Al-Qasr (a fort or a huge log of wood) ." (V.77:32)
Narrated Ibn `Abbas:
حَدَّثَنَا مُحَمَّدُ بْنُ كَثِيرٍ ، أَخْبَرَنَا سُفْيَانُ ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ عَابِسٍ ، قَالَ سَمِعْتُ ابْنَ عَبَّاسٍ ، إِنَّهَا تَرْمِي بِشَرَرٍ كَالْقَصْرِ قَالَ كُنَّا نَرْفَعُ الْخَشَبَ بِقَصَرٍ ثَلاَثَةَ أَذْرُعٍ أَوْ أَقَلَّ، فَنَرْفَعُهُ لِلشِّتَاءِ فَنُسَمِّيهِ الْقَصَرَ.
(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.