Complex sentence: According to Tabari, he was told "If you accept Islam, the Messenger of God will not kill you" (according to Tabari's version of the event), he accepted Islam out of his own free will, and was allowed to go free.
Split into simpler sentences: According to Tabari, he was told "If you accept Islam, the Messenger of God will not kill you" (according to Tabari's version of the event). He accepted Islam out of his own free will, and was allowed to go free.