Sahih Bukhari Volume 003, Book 041, Hadith Number 590.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 41. Loans, Payment of Loans, Freezing of Property, Bankruptcy.
Narated By Ibn 'Umar : A man came to the Prophet and said, "I am often betrayed in bargaining." The Prophet advised him, "When you buy something, say (to the seller), 'No deception." The man used to say so afterwards.