Language:
كتاب الجهاد والسير
56  
Fighting for the Cause of Allah (Jihaad)
(149)
Chapter: Not to punish with Allah's punishment
(149)
باب لاَ يُعَذَّبُ بِعَذَابِ اللَّهِ
Sahih al-Bukhari 3017

Narrated `Ikrima:

`Ali burnt some people and this news reached Ibn `Abbas, who said, "Had I been in his place I would not have burnt them, as the Prophet (ﷺ) said, 'Don't punish (anybody) with Allah's Punishment.' No doubt, I would have killed them, for the Prophet (ﷺ) said, 'If somebody (a Muslim) discards his religion, kill him.' "

حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا سُفْيَانُ، عَنْ أَيُّوبَ، عَنْ عِكْرِمَةَ، أَنَّ عَلِيًّا ـ رضى الله عنه ـ حَرَّقَ قَوْمًا، فَبَلَغَ ابْنَ عَبَّاسٍ فَقَالَ لَوْ كُنْتُ أَنَا لَمْ أُحَرِّقْهُمْ، لأَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ ‏"‏ لاَ تُعَذِّبُوا بِعَذَابِ اللَّهِ ‏"‏‏.‏ وَلَقَتَلْتُهُمْ كَمَا قَالَ النَّبِيُّ صلى الله عليه وسلم ‏"‏ مَنْ بَدَّلَ دِينَهُ فَاقْتُلُوهُ ‏"‏‏.‏
Reference : Sahih al-Bukhari 3017
In-book reference : Book 56, Hadith 226
USC-MSA web (English) reference : Vol. 4, Book 52, Hadith 260
  (deprecated numbering scheme)