Al-Hāfidh Ibn Hajr (rahimahullāh) said:
1001: `Ā’ishah (رضي الله عنها) said: A man divorced his wife on three occasions, so another man married her. Then he divorced her before having sexual relations with her. The first husband now wished to remarry her. So Allah’s Messenger (ﷺ) was asked about that. So he said: “No, he cannot until the second husband has enjoyed sexual relations with her as her first husband had.” Reported by Bukhāri (5261) and Muslim, and this is the wording of Muslim.
We have already preceded with the discussion concerning the woman who has been divorced three times by her husband – that it is not permitted for him to marry her, except after she has married another man with a desire to marry him (and intent to remain with him) and not just a marriage of convenience to make her permissible for her previous husband (zawāj tahleel). So then if this second husband divorces her, and her ‘iddah comes to an end, her first husband is allowed to marry her. However, if a man marries her with a sound marriage contract without the intent of marrying her to divorce her to make her halāl for her previous husband, and without deceit, and he really wishes to marry her, but he divorces her before consummating the marriage, then it is not permissible for her to marry the first husband. That is due what this hadeeth states: that a man divorced his wife thrice. Then another man married her but divorced her before having sexual relations with her. Then the first husband wished to marry her again. So the Prophet (ﷺ) was asked regarding that, so he said, “No.” Meaning it is not allowed for him – and then he mentioned the reason saying “not until until the second husband has enjoyed sexual relations with her as her first husband had.” So a marriage contract is not sufficient on its own – sexual relations must take place after the marriage contract – and sexual relations occur by penetration, i.e. intercourse, even if he does not ejaculate. That is because he has by this attained gratification. The term “that he may enjoy her ‘usailah,“ in the hadeeth refers to a diminution of the term al-‘asal (honey), i.e. her honey. Here sexual intercourse is referred to as honey because of what is in this intimate act of sweetness between the husband and wife, just like the sweetness of honey.
This hadeeth is a proof that it is not sufficient for a thrice divorced woman to be made permissible to her previous husband just on the basis of a marriage contract with another man – rather sexual intercourse must have taken place with the new husband. Touching, kissing, and sex without penetration is not sufficient.
Title: Kitābun-Nikāh (The Book of Marriage) from Shaikh Sālih al-Fawzān’s explanation of Buloogh al-Marām min Adillatil-Ahkām of Al-Hāfidh Ahmad Ibn ‘Ali Ibn Hajr al-Asqalānee (Born 773H, Died 852H), entitled Tas-heel al-Ilmām bi-fiqhil-Ahādeeth min Bulooghil-Marām and is printed in seven volumes. A translation of this important and very enlightening chapter adapted in places for brevity and simplicity (volume 4, no. 1001 and in English, no. 854)