Bismillah Walhamdulillah Was Salaatu Was Salaam ‘ala Rasulillah Narrated Ibn ‘Umar (Radi-Allahu ‘anhu):
A man came to the Prophet (Sallallahu ‘Alaihi Wa Sallam) and said, “I am often betrayed in bargaining.” The Prophet (Sallallahu ‘Alaihi Wa Sallam) advised him, “When you buy something, say (to the seller), ‘No deception.’” The man used to say so afterwards.
Bukhari Vol. 3 : No. 590