كتاب الإيمان
1  
The Book of Faith
(90)
Chapter: The Intercession of the Prophet (saws) for Abu Talib and the reduction of his punishment as a result
(90)
باب شَفَاعَةِ النَّبِيِّ صلى الله عليه وسلم لأَبِي طَالِبٍ وَالتَّخْفِيفِ عَنْهُ بِسَبَبِهِ ‏‏
Sahih Muslim 210

Abu Sa'id al-Khudri reported:

A mention was made of his uncle Abu Talib before the Messenger of Allah (ﷺ) He said: My intercession may benefit him on the Day of Resurrection and he may be placed in the shallow part of the Fire which would reach his ankles and his brain would be boiling.
وَحَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا لَيْثٌ، عَنِ ابْنِ الْهَادِ، عَنْ عَبْدِ اللَّهِ بْنِ خَبَّابٍ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم ذُكِرَ عِنْدَهُ عَمُّهُ أَبُو طَالِبٍ فَقَالَ ‏ "‏ لَعَلَّهُ تَنْفَعُهُ شَفَاعَتِي يَوْمَ الْقِيَامَةِ فَيُجْعَلُ فِي ضَحْضَاحٍ مِنْ نَارٍ يَبْلُغُ كَعْبَيْهِ يَغْلِي مِنْهُ دِمَاغُهُ ‏"‏ ‏.‏
Reference : Sahih Muslim 210
In-book reference : Book 1, Hadith 419
USC-MSA web (English) reference : Book 1, Hadith 411
  (deprecated numbering scheme)