Ali (may Allah be pleased with him) said: The apostate is to be given the chance to repent three times. Then he recited this verse: "Indeed, those who believed, then disbelieved, then believed, then disbelieved, then increased in disbelief" [Surah al-Nisa: 137].
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المرتد / 16889
Ali (may Allah be pleased with him) said: The apostate is to be given the chance to repent three times; if he goes back (to disbelief), he is to be killed.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المرتد / 16890
Abu Ali al-Hamdani said: A man who had apostatised was brought to Fadalah bin Ubayd (may Allah be pleased with him). He invited him to Islam and he became a Muslim, but then he apostatised again. When this happened three times, he cited this verse as proof: "Indeed, those who believed, then disbelieved, then believed, then disbelieved, then increased in disbelief, Allah will never forgive them, nor guide them to a way" [Surah al-Nisa: 137], and had him killed.
There is weakness in the chains of these reports, and the verse concerns one who remains firm upon disbelief. We have narrated with a mursal chain that the Messenger of Allah (peace and blessings be upon him) asked Nabhan to repent four times, each time after he had joined the polytheists; and the apparent meaning of the authentic reports about what protects (a person's) blood supports this mursal report and agrees with it. And Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المرتد / 16892