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 ".
Bukhari
Fighting for the Cause of Allah (Jihaad) • Hadith 226