The Book of Marriage
16/17. Chapter:
It is not permissible for a woman who has been thrice-divorced to return to the one who divorced her until she marries another husband who has intercourse with her, then divorces her, and she completes the 'Iddah
Sahih Muslim
حَدَّثَنَا مُحَمَّدُ بْنُ الْعَلاَءِ الْهَمْدَانِيُّ، حَدَّثَنَا أَبُو أُسَامَةَ، عَنْ هِشَامٍ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم سُئِلَ عَنِ الْمَرْأَةِ يَتَزَوَّجُهَا الرَّجُلُ فَيُطَلِّقُهَا فَتَتَزَوَّجُ رَجُلاً فَيُطَلِّقُهَا قَبْلَ أَنْ يَدْخُلَ بِهَا أَتَحِلُّ لِزَوْجِهَا الأَوَّلِ قَالَ " لاَ حَتَّى يَذُوقَ عُسَيْلَتَهَا ".
'A'isha (Allah be pleased with her) reported that Allah's Messenger (ﷺ) was asked about a woman whom a man married and then divorced her, and then she married (another) person, and she was divorced before sexual intercourse with her, whether it was lawful for her first husband (to marry her in this state). He (the Holy Prophet) said: No, until he has tasted her sweetness.
Reference : Sahih Muslim 1433dIn-book reference : Book 16, Hadith 131USC-MSA web (English) reference : Book 8, Hadith 3357