Sahih al-Bukhari, Volume 4, Book 52, Hadith 260 (USC-MSA) ⓘ

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 said, 'Don't punish (anybody) with Allah's Punishment.' No doubt, I would have killed them, for the Prophet 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 ‏"‏‏.‏