Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Abdullah ibn Abbas (may Allah be pleased with them both), he says: A man from the Ansari tribe accepted Islam and then became an apostate and joined the polytheists. Later, he became remorseful for what he had done and sent a message to his people, saying: Ask the Messenger of Allah (peace and blessings be upon him) whether there is repentance for him? So his people came to the Messenger of Allah (peace and blessings be upon him) and said: Indeed, so-and-so has felt regret and has instructed us to ask you whether there is any repentance for him? Then this verse was revealed: "How shall Allah guide a people who disbelieved after their belief..." The verse was recited up to "Most Forgiving, Most Merciful." So the people sent a message to him, and he became Muslim again.