ENOfficial
Narrated Abdullah ibn Abbas: When the Prophet (ﷺ) ordered a man and his wife to invoke curses on each other, he ordered a man to put his hand on his mouth when he came to the fifth utterance, saying that it would be the deciding one.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا مَخْلَدُ بْنُ خَالِدٍ الشَّعِيرِيُّ، حَدَّثَنَا سُفْيَانُ، عَنْ عَاصِمِ بْنِ كُلَيْبٍ، عَنْ أَبِيهِ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلم أَمَرَ رَجُلاً حِينَ أَمَرَ الْمُتَلاَعِنَيْنِ أَنْ يَتَلاَعَنَا أَنْ يَضَعَ يَدَهُ عَلَى فِيهِ عِنْدَ الْخَامِسَةِ يَقُولُ إِنَّهَا مُوجِبَةٌ .
sunnah.com