Sahih Bukhari Volume 9, Book 93, Hadith 7168

حَدَّثَنَا يَحْيَى، حَدَّثَنَا عَبْدُ الرَّزَّاقِ، أَخْبَرَنَا ابْنُ جُرَيْجٍ، أَخْبَرَنِي ابْنُ شِهَابٍ، عَنْ سَهْلٍ، أَخِي بَنِي سَاعِدَةَ أَنَّ رَجُلاً، مِنَ الأَنْصَارِ جَاءَ إِلَى النَّبِيِّ صلى الله عليه وسلم فَقَالَ أَرَأَيْتَ رَجُلاً وَجَدَ مَعَ امْرَأَتِهِ رَجُلاً، أَيَقْتُلُهُ فَتَلاَعَنَا فِي الْمَسْجِدِ وَأَنَا شَاهِدٌ‏.‏

Narrated By Sahl : (The brother of Bani Sa'ida) A man from the Ansar came to the Prophet and said, "If a man finds another man sleeping with his wife, should he kill him?" That man and his wife then did Lian in the mosque while I was present.