Narrated Ibn 'Umar:
A man told the Messenger of Allah ﷺ that he was being deceived in business transactions. The Messenger of Allah ﷺ then said: When you make a bargain, say: There is no attempt to deceive. So when the man made a bargain, he said: There is no attempt to deceive.

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، عَنْ مَالِكٍ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَجُلاً، ذَكَرَ لِرَسُولِ اللَّهِ ﷺ أَنَّهُ يُخْدَعُ فِي الْبَيْعِ فَقَالَ لَهُ رَسُولُ اللَّهِ ﷺ " إِذَا بَايَعْتَ فَقُلْ لاَ خِلاَبَةَ " . فَكَانَ الرَّجُلُ إِذَا بَايَعَ يَقُولُ لاَ خِلاَبَةَ .