It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that he mentioned some people whom Sayyiduna Ali (may Allah be pleased with him) had burned, so he said: If I had been there, I would not have burned them, because the Messenger of Allah (peace and blessings be upon him) said: "Do not punish anyone with Allah's punishment (i.e., fire)." And I would certainly have killed them, and also because the Messenger of Allah (peace and blessings be upon him) said: "Whoever changes his religion, kill him."
Hadith Referenceمسند اسحاق بن راهويه / كتاب الجهاد / 535
Hadith Takhrij«بخاري ، كتاب الجهاد والسير ، باب لا يعذب بعذاب الله ، رقم : 3016 . سنن ابوداود ، رقم : 4351 . سنن ترمذي ، رقم : 1485 . صحيح ابن حبان ، رقم : 5606 .»
Explanation & Benefits
Hafiz Abdush Shakoor Tirmidhi
Benefits: From the aforementioned hadith, it is understood that punishing with fire is not permissible for anyone. This is something exclusive to Allah, the Possessor of Majesty. When the statement of Sayyiduna Abdullah ibn Abbas radi Allahu anhuma reached Sayyiduna Ali radi Allahu anhu, he said: Ibn Abbas radi Allahu anhuma has spoken the truth. (Sunan Tirmidhi, No. 1458)
It is also understood that if a person, after accepting Islam, enters into disbelief again, then he is liable to be killed. However, before punishing the apostate (murtad), he should be asked to repent; if he repents, then fine, otherwise he should be killed.
It is mentioned in "Sunan Abi Dawud" that a man who had apostatized from Islam was brought before Sayyiduna Abu Musa Ash'ari radi Allahu anhu. He radi Allahu anhu invited him for about twenty nights. Then Sayyiduna Mu'adh radi Allahu anhu arrived and he also invited him, but he refused, so his neck was struck (he was executed). (Sunan Abi Dawud, Kitab al-Hudud, No. 4356) Thus, it is understood that after giving a thorough invitation to Islam and establishing the proof, the apostate is liable to be killed.