أَخْبَرَنَا عَلِيُّ بْنُ مَيْمُونٍ، قَالَ 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 عِنْدَ الْخَامِسَةِ عَلَى فِيهِ وَقَالَ " إِنَّهَا مُوجِبَةٌ " .
It was narrated from Ibn 'Abbas: "When the Prophet commanded the two who were engaging in Li'an to utter the fifth oath, he commanded a man to place his hand over his mouth, and he said: "It will inevitably bring the punishment upon the liar."" Translation Not Available
Book Ref: Sunan An Nisai Book 27 Hadith 3472
Web Ref: Sunan An Nisai Vol 4 Book 27 Hadith 3502