If he divorces her (for the third time), it is unlawful for him to remarry her, unless she marries another man, then he divorces her. The first husband can then remarry her, so long as they observe God’s laws. These are God’s laws; He explains them for people who know.
فَإِن طَلَّقَها فَلا تَحِلُّ لَهُ مِن بَعدُ حَتّىٰ تَنكِحَ زَوجًا غَيرَهُ فَإِن طَلَّقَها فَلا جُناحَ عَلَيهِما أَن يَتَراجَعا إِن ظَنّا أَن يُقيما حُدودَ اللَّهِ وَتِلكَ حُدودُ اللَّهِ يُبَيِّنُها لِقَومٍ يَعلَمونَ
fa in tallaqahaa falaa tahillu lahoo mim ba’du hattaa tankiha zawjan ghairah; fa in tallaqahaa falaa junaaha ‘alaihimaaa ai yataraaja’aaa in zannaaa ai yuqeemaa hudoodal laa; wa tilka hudoodul laahi yubaiyinuhaa liqawminy ya’lamoon