Heretics (zanadiqah): what is their hadd punishment?

Suwayd bin Ghaflah reports that Sayyiduna Ali (may Allah be pleased with him) burned heretics in the marketplace. When he cast the fire upon them, he said: "Allah and His Messenger (peace and blessings be upon him) spoke the truth." Then he went back. The narrator says: I followed behind him, and he turned to me and asked: "Is it Suwayd?" I said: "Yes, O Commander of the Believers. I heard you saying something." He said: "O Suwayd, I am among ignorant people. So when you hear me say: 'The Messenger of Allah (peace and blessings be upon him) said,' then it is the truth."

Abd al-Rahman bin Ubayd reports that Ubayd said: There were some people who used to take the annual and monthly stipends and pray with the people, and they also worshipped idols in secret. These people were brought to Sayyiduna Ali (may Allah be pleased with him), and he put them in the mosque, or in the prison. Then he said: "O people, what is your opinion about those who take the annual and monthly stipends with you and also worship these idols?" The people said: "Kill them." He said: "No, but I will deal with them as was done to our father Ibrahim (peace be upon him)." So he burned them in the fire.

Ayyub bin Nu'man reports: I was present with Sayyiduna Ali (may Allah be pleased with him) in the open square when a man came and said: "O Commander of the Believers, here there is a household with an idol in their house, which they worship." So Sayyiduna Ali (may Allah be pleased with him) stood up and began walking until he reached that house. He gave the people an order, so they went in and brought out to him a marble statue. Then Sayyiduna Ali (may Allah be pleased with him) burned that house.

Sayyiduna Mukhariq (may Allah be pleased with him) says that Sayyiduna Ali (may Allah be pleased with him) sent Muhammad bin Abi Bakr as governor over Egypt. Muhammad then wrote to Sayyiduna Ali (may Allah be pleased with him), asking him about the zindiqs: "Some of them worship the sun and the moon, some of them worship other things, and some of them claim Islam. What is the ruling concerning them?" Sayyiduna Ali (may Allah be pleased with him) wrote back and commanded him concerning the zindiqs that he should kill those who claim Islam and leave all the rest to worship whatever they wish.

Ikrimah says that news reached Sayyiduna Ibn Abbas (may Allah be pleased with them both) that Sayyiduna Ali (may Allah be pleased with him) had seized some zindiqs and burned them. He said: "As for me, I would not punish them with the manner of Allah's punishment; had it been me, I would have killed them, because of the saying of the Prophet (peace and blessings be upon him): 'Whoever changes his religion, kill him.'"