مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2539
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated from ‘Ikrimah that ‘Ali caught some people who had apostatised from Islam, and he burned them with fire. News of that reached Ibn Abbas (رضي الله عنه) and he said: If it were me, I would not have burned them. The Messenger of Allah (ﷺ) said: "Do not punish anyone with the punishment of Allah, may He be glorified and exalted.” And the Messenger of Allah (ﷺ) said: “Whoever changes his religion, execute him." News of what Ibn 'Abbas said reached ‘Ali and he said: Woe to the son of the mother of Ibn 'Abbas!
Musnad Ahmad 2552lts isnad is saheeh, al-Bukhari (3017)]