Compiled by Imam Muhammad al-Bukhari
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 ".
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."