Full Sharh — Sahih al-Bukhari 6922
حَدَّثَنَا أَبُو النُّعْمَانِ، مُحَمَّدُ بْنُ الْفَضْلِ حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، عَنْ أَيُّوبَ، عَنْ عِكْرِمَةَ، قَالَ أُتِيَ عَلِيٌّ ـ رضى الله عنه ـ بِزَنَادِقَةٍ فَأَحْرَقَهُمْ فَبَلَغَ ذَلِكَ ابْنَ عَبَّاسٍ فَقَالَ لَوْ كُنْتُ أَنَا لَمْ أُحْرِقْهُمْ لِنَهْىِ رَسُولِ اللَّهِ صلى الله عليه وسلم وَلَقَتَلْتُهُمْ لِقَوْلِ رَسُولِ اللَّهِ صلى الله عليه وسلم " مَنْ بَدَّلَ دِينَهُ فَاقْتُلُوهُ ".
English Translation
Narrated `Ikrima:Some Zanadiqa (atheists) were brought to `Ali and he burnt them. The news of this event, reached Ibn `Abbas who said, "If I had been in his place, I would not have burnt them, as Allah's Messenger (ﷺ) forbade it, saying, 'Do not punish anybody with Allah's punishment (fire).' I would have killed them according to the statement of Allah's Messenger (ﷺ), 'Whoever changed his Islamic religion, then kill him
Source
Sahih al-Bukhari(صحيح البخاري)
Apostates
Hadith Number
6922