(12) باب الْخَدِيعَةِ فِي الْبَيْعِ
It was narrated from Anas that:
there was a man whose mental faculties were lacking, and he used to buy and sell. His family came to the Prophet and said: "O Prophet of Allah stop him." So the Prophet of Allah called him, and told him not to do that. He said: "O Prophet of Allah, I cannot bear to be away from business," He said "If you engaged in a deal then say: 'There is no intention to deceive. "' (Sahih )
Reference: Sunan an-Nasa'i 4485
In-book reference: Book 44, Hadith 37
English translation: Vol. 5, Book 44, Hadith 4490