Narrated Abu Hurairah (RA):

Allah's Messenger (ﷺ) 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." [Reported by al-Arba'a except an-Nasa'i. al-Hakim graded it Sahih (authentic)].

وَعَنْ أَبِي هُرَيْرَةَ ‏- رضى الله عنه ‏- قَالَ : قَالَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-{ ثَلَاثٌ جِدُّهنَّ جِدٌّ , وَهَزْلُهُنَّ جِدٌّ : اَلنِّكَاحُ , وَالطَّلَاقُ , وَالرَّجْعَةُ } رَوَاهُ اَلْأَرْبَعَةُ إِلَّا النَّسَائِيَّ , وَصَحَّحَهُ اَلْحَاكِمُ [1]‏ .‏