Language:
كتاب البيوع
34  
Sales and Trade
(48)
Chapter: What is disliked as regards cheating in business
(48)
باب مَا يُكْرَهُ مِنَ الْخِدَاعِ فِي الْبَيْعِ
Sahih al-Bukhari 2117

Narrated `Abdullah bin `Umar:

A person came to the Prophet (ﷺ) and told him that he was always betrayed in purchasing. The Prophet (ﷺ) told him to say at the time of buying, "No cheating."

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، أَخْبَرَنَا مَالِكٌ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ أَنَّ رَجُلاً، ذَكَرَ لِلنَّبِيِّ صلى الله عليه وسلم أَنَّهُ يُخْدَعُ فِي الْبُيُوعِ، فَقَالَ ‏ "‏ إِذَا بَايَعْتَ فَقُلْ لاَ خِلاَبَةَ ‏"‏‏.‏
Reference : Sahih al-Bukhari 2117
In-book reference : Book 34, Hadith 70
USC-MSA web (English) reference : Vol. 3, Book 34, Hadith 328
  (deprecated numbering scheme)