It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that a man from the Ansar embraced Islam, then apostatized and joined the polytheists. Then he regretted it and sent word to his people: Ask the Messenger of Allah (peace and blessings be upon him): Is there any room for repentance for me? So these verses were revealed: "How shall Allah guide a people who disbelieved after their belief" up to His saying: "Except those who repent after that and reform themselves, for indeed Allah is Most Forgiving, Most Merciful." [Al Imran: 86-89] . The narrator said: Then his people sent word to him, and he embraced Islam (again). This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.