Hazrat Ikrimah narrates that Hazrat Ibn Abbas (may Allah be pleased with them both) received news that Hazrat Ali (may Allah be pleased with him) had captured some heretics and burned them. So he said: As far as I am concerned, I would not punish them with the punishment of Allah, and if I were in that position, I would have killed them. Because of the hadith of the Noble Prophet (peace and blessings be upon him): Whoever changes his religion, kill him.