وَعَنِ اِبْنِ عُمَرَ رَضِيَ اَللَّهُ عَنْهُمَا
قَالَ: ذَكَرَ رَجُلٌ لِلنَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَنَّهُ يُخْدَعُ فِي اَلْبُيُوعِ فَقَالَ: «إِذَا بَايَعْتَ فَقُلْ: لَا خَلَابَةَ»
A man told the Messenger of Allah (sallallahu alayhi wa sallam) that he was being deceived (cheated) in business transactions, and he replied, “When you make a purchase say, ‘Deceiving (cheating) is not allowed (i.e. he has the choice to return the goods if he wills).’”.
Bulugh al-Maram 950, Book 7, Business Transactions, Hadith 61. 1 min read