The Cow - 2:230
If he divorces her again (for the third time), she is not lawful for him after that unless she marries another. There is no harm in their returning to each other if they believe that they will observe the law of Allah. This is the law of Allah; We have made it clear for a people who know.
Whoever transgresses the law of Allah:
Divorce/65:1
O Prophet, when you divorce women, observe the term of divorce and calculate it well. Listen to Allah, your Lord. And do not drive them out of their homes, nor should they drive them out (do not force them to do so by ill-treatment). Except if they commit proven adultery. This is the law of Allah. Whoever transgresses Allah´s law has wronged himself. You do not know, but perhaps Allah will bring about something (positive) after that.