Sahih al-Bukhari, Hadith 6964 ⓘ
Narrated `Abdullah bin `Umar: A man mentioned to the Prophet that he had always been cheated in bargains. The Prophet said, "Whenever you do bargain, say, 'No cheating.'"
حَدَّثَنَا إِسْمَاعِيلُ، حَدَّثَنَا 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 " .
also referenced under: Book 90, Hadith 11 (In-Book) & Volume 9, Book 86, Hadith 94 (USC-MSA)