Sahih al-Bukhari 6964

Arabic

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 ‏"‏‏.‏

English translation

Narrated `Abdullah bin `Umar:A man mentioned to the Prophet (ﷺ) that he had always been cheated in bargains. The Prophet (ﷺ) said, "Whenever you do bargain, say, 'No cheating

Reference: Sahih al-Bukhari 6964, Book of Tricks. English translation by Dr. Muhammad Muhsin Khan.