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

In this report, he said: He divorced her three times in the presence of the Messenger of Allah (ﷺ), and the Messenger of Allah (ﷺ) upheld it, and what was done in the presence of the Prophet (ﷺ) became a Sunnah. Sahl said: I was present at this before the Messenger of Allah (ﷺ), and the Sunnah subsequently proceeded regarding those who engage in li'an (mutual imprecation) that they are separated and will never be joined together again.