Sunan Abi Dawud, Hadith 2189 ⓘ
Narrated AbuHurayrah: The Prophet said: There are three things which, whether undertaken seriously or in jest, are treated as serious: Marriage, divorce and taking back a wife (after a divorce which is not final)
حَدَّثَنَا الْقَعْنَبِيُّ، حَدَّثَنَا عَبْدُ الْعَزِيزِ، - يَعْنِي ابْنَ مُحَمَّدٍ - عَنْ عَبْدِ الرَّحْمَنِ بْنِ حَبِيبٍ، عَنْ عَطَاءِ بْنِ أَبِي رَبَاحٍ، عَنِ ابْنِ مَاهَكَ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " ثَلاَثٌ جِدُّهُنَّ جِدٌّ وَهَزْلُهُنَّ جِدٌّ النِّكَاحُ وَالطَّلاَقُ وَالرَّجْعَةُ " .
also referenced under: Hadith 2194 (DarusSalam) & Book 12, Hadith 2189 (USC-MSA)