{ If a man divorces a woman, then she is no longer lawful to him after that until she has marital relations with a husband other than him } Al-baqara 230

The word of the Most High { If a man divorces a woman } : meaning the third pronouncement of divorce; { Then she is no longer lawful to him after that } : that is, after the third pronouncement; { Until she has marital relations with a husband other than him } : other than the divorcer, and this man has sex with her, since marital relations [nikah] assumes intercourse.