The ruling on the apostate

Amr bin Shu'ayb narrates from his father, and he from his grandfather (Sayyiduna Abdullah bin Amr bin al-As), that Sayyiduna Amr bin al-As (may Allah be pleased with him) sent a letter to the Commander of the Believers, Sayyiduna Umar al-Faruq (may Allah be pleased with him), in which he asked about a man who accepted Islam and then adopted disbelief, then embraced Islam again and then became a disbeliever, and did so repeatedly, many times. Would his Islam (still) be accepted? Sayyiduna Umar (may Allah be pleased with him) wrote to him in reply, "Accept from them what Allah accepts from them; present Islam to him, and if he accepts it (well and good), otherwise strike his neck."

Imam al-Humaydi narrated through Sufyan and Imran bin Zibyan from a man of Banu Hanifah, who said: Sayyiduna Abu Hurayrah (may Allah be pleased with him) asked me, "Do you know al-Rajjal (bin Unfuwah)?" I said, "Yes." He said, "Indeed, I heard the Messenger of Allah (peace and blessings be upon him) say, 'His (al-Rajjal's) molar tooth in the Fire will be bigger than (the mountain of) Uhud.'" The narrator said: That man had first accepted Islam, but later apostatised and joined Musaylimah the Liar, and he had said (out of tribal partisanship): "Two rams are butting each other, and the one dearer to me of the two is the one that wins, that is, my own ram (Musaylimah the Liar)."
This hadith describes the terrible end of this wretched man named al-Rajjal bin Unfuwah, who, despite having attained the company of the Prophet, sided with the trial of apostasy and affirmed the false prophethood of Musaylimah, as a result of which he was warned of the dreadful punishment of Hell.

It is narrated from Imam Abu Ya'la (may Allah have mercy on him) that Amir al-Sha'bi (may Allah have mercy on him) said: When the Messenger of Allah (peace and blessings be upon him) passed away and (at the time of the trial of apostasy) those who were to apostatise did so, Sayyiduna Adi bin Hatim (may Allah be pleased with him) stood up (in support of the truth) with a thousand men of the tribe of Tayyi'; meanwhile Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) sent Sayyiduna Khalid bin al-Walid (may Allah be pleased with him) on the campaign to al-Yamamah. The narrator said: Banu Amir had killed the agents appointed by the Messenger of Allah (peace and blessings be upon him) and burned them with fire, so Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) wrote a letter to Sayyiduna Khalid bin al-Walid (may Allah be pleased with him): "Kill these criminals of Banu Amir and burn them with fire." He carried out this order until their women cried out in lament. Then he advanced until he reached a watering place, and the people there came out to face him. He cried out in a loud voice, 'Allahu akbar, Allahu akbar' (Allah is the Greatest, Allah is the Greatest), and those people called out, "We bear witness that there is no god worthy of worship except Allah, and we bear witness that Muhammad (peace and blessings be upon him) is the Messenger of Allah." When Sayyiduna Khalid bin al-Walid (may Allah be pleased with him) heard these words of testimony from their tongues, he held back from taking action against them.