Translation
(93) Judgments (Ahkaam)
كتاب الأحكام
(18) Chapter: Whoever gave judgements of Li'an in the mosque
(18) باب مَنْ قَضَى وَلاَعَنَ فِي الْمَسْجِدِ
Sahih al-Bukhari 7165 

Narrated Sahl bin Sa`d:

I witnessed a husband and a wife who were involved in a case of Lian. Then (the judgment of) divorce was passed. I was fifteen years of age, at that time.

حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا سُفْيَانُ، قَالَ الزُّهْرِيُّ عَنْ سَهْلِ بْنِ سَعْدٍ، قَالَ شَهِدْتُ الْمُتَلاَعِنَيْنِ وَأَنَا ابْنُ خَمْسَ، عَشْرَةَ فُرِّقَ بَيْنَهُمَا‏.‏
Reference : Sahih al-Bukhari 7165
In-book reference : Book 93, Hadith 29
USC-MSA web (English) reference : Vol. 9, Book 89, Hadith 278
  (deprecated numbering scheme)