Muwatta Malik, Book 31, Hadith 1385 (In-Book) ⓘ

Yahya related to me from Malik from Abdullah ibn Dinar from Abdullah ibn Umar that a man mentioned to the Messenger of Allah, may Allah bless him and grant him peace, that he was always being cheated in business transactions. The Messenger of Allah, may Allah bless him and grant him peace, said, "When you enter a transaction, say, 'No trickery.' So whenever that man entered a transaction, he would say, 'No trickery.' "

حَدَّثَنِي يَحْيَى، عَنْ مَالِكٍ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ، أَنَّ رَجُلاً، ذَكَرَ لِرَسُولِ اللَّهِ صلى الله عليه وسلم أَنَّهُ يُخْدَعُ فِي الْبُيُوعِ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ إِذَا بَايَعْتَ فَقُلْ لاَ خِلاَبَةَ ‏" ‏ ‏.‏ قَالَ فَكَانَ الرَّجُلُ إِذَا بَايَعَ يَقُولُ لاَ خِلاَبَةَ ‏.‏