(19) باب مَا يُنْهَى عَنْ إِضَاعَةِ الْمَالِ
Narrated Ibn `Umar:
A man came to the Prophet (ﷺ) and said, "I am often betrayed in bargaining." The Prophet (ﷺ) advised him, "When you buy something, say (to the seller), 'No deception." The man used to say so afterwards.
Reference: Sahih al-Bukhari 2407
In-book reference: Book 43, Hadith 22
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 41, Hadith 590