كتاب البيوع
11  
Business Transactions
(3a)
Chapter: Conditional Bargains* - Section 1
(3)
باب الخيار - الفصل الأول
Mishkat al-Masabih 2803
Ibn ‘Umar said that a man told the Prophet that he was being deceived in business transactions, and he replied, "When you make a bargain say, 'There is no attempt to deceive'*.” Then the man made a habit of saying that. (Bukhari and Muslim.) * He was to say this to protect himself because he was not expert enough to detect defects in what he was buying. Some hold that one who says this has the right to cancel the transaction if any defect is discovered within three days. Some say this applied only to the man who spoke to the Prophet; others say it applies to anyone.
وَعَنِ ابْنِ عُمَرَ قَالَ: قَالَ رَجُلٌ لِلنَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِنِّي أُخْدَعُ فِي الْبُيُوعِ فَقَالَ: " إِذَا بَايَعْتَ فَقُلْ: لَا خلابة " فَكَانَ الرجل يَقُوله
  مُتَّفَقٌ عَلَيْهِ   (الألباني) حكم   :
Reference : Mishkat al-Masabih 2803
In-book reference : Book 11, Hadith 42