It was narrated from 'Ikrimah that

Some of these heretics were brought to ‘Ali and they had some books with them. He issued orders that a fire be lit, then he burned them and their books. News of that reached Ibn 'Abbas (رضي الله عنه) and he said: If it were me, I would not have burned them because the Messenger of Allah (ﷺ) forbade it; but I would have executed them because the Messenger of Allah (ﷺ) said: “Whoever changes his religion, execute him.” And the Messenger of Allah (ﷺ) said: "Do not punish with the punishment of Allah, may He be glorified and exalted.”