(2) باب حُكْمِ الْمُرْتَدِّ وَالْمُرْتَدَّةِ
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.'"
Reference: Sahih al-Bukhari 6922
In-book reference: Book 88, Hadith 5
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 9, Book 84, Hadith 57