Sahih Bukhari Volume 9, Book 93, Hadith 7186

فَجَاءَ الأَشْعَثُ وَعَبْدُ اللَّهِ يُحَدِّثُهُمْ فَقَالَ فِيَّ نَزَلَتْ وَفِي رَجُلٍ خَاصَمْتُهُ فِي بِئْرٍ فَقَالَ النَّبِيُّ صلى الله عليه وسلم ‏"‏ أَلَكَ بَيِّنَةٌ ‏"‏‏.‏ قُلْتُ لاَ‏.‏ قَالَ ‏"‏ فَلْيَحْلِفْ ‏"‏‏.‏ قُلْتُ إِذًا يَحْلِفُ‏.‏ فَنَزَلَتْ ‏{‏إِنَّ الَّذِينَ يَشْتَرُونَ بِعَهْدِ اللَّهِ‏}‏ الآيَةَ‏

'Al-Ashath came while Abdullah was narrating (this) to the people. Al-Ashath said, "This verse was revealed regarding me and another man with whom I had a quarrel about a well. The Prophet said (to me), "Do you have any evidence?' I replied, 'No.' He said, 'Let your opponent take an oath.' I said: I am sure he would take a (false) oath." Thereupon it was revealed: 'Verily! those who purchase a small gain at the cost of Allah's Covenant...' (3.77)