The tradition mentioned above has also been transmitted by Sahl bin Sa’d Al Sa’idi through a different chain of narrators. This version has “He divorced her three times before the Messenger of Allah (ﷺ). The Messenger of Allah (ﷺ) implemented it and what is done before the Prophet (ﷺ) is sunnah(model behavior of the Prophet). Sahl said “I attended this before the Messenger of Allah(ﷺ). Afterwards the sunnah about those who invoked curses on each other was established that they (the spouses) were separated from each other and they would never be united.”
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا أَحْمَدُ بْنُ عَمْرِو بْنِ السَّرْحِ، حَدَّثَنَا ابْنُ وَهْبٍ، عَنْ عِيَاضِ بْنِ عَبْدِ اللَّهِ الْفِهْرِيِّ، وَغَيْرِهِ، عَنِ ابْنِ شِهَابٍ، عَنْ سَهْلِ بْنِ سَعْدٍ، فِي هَذَا الْخَبَرِ قَالَ فَطَلَّقَهَا ثَلاَثَ تَطْلِيقَاتٍ عِنْدَ رَسُولِ اللَّهِ صلى الله عليه وسلم فَأَنْفَذَهُ رَسُولُ اللَّهِ صلى الله عليه وسلم وَكَانَ مَا صُنِعَ عِنْدَ النَّبِيِّ صلى الله عليه وسلم سُنَّةً . قَالَ سَهْلٌ حَضَرْتُ هَذَا عِنْدَ رَسُولِ اللَّهِ صلى الله عليه وسلم فَمَضَتِ السُّنَّةُ بَعْدُ فِي الْمُتَلاَعِنَيْنِ أَنْ يُفَرَّقَ بَيْنَهُمَا ثُمَّ لاَ يَجْتَمِعَانِ أَبَدًا .
sunnah.com