Hadith 2414
Narrated Ibn `Umar: A man was often cheated in buying. The Prophet said to him, "When you buy something, say (to the seller), No cheating." The man used to say so thenceforward .
Hadith 2415
Narrated Jabir: A man manumitted a slave and he had no other property than that, so the Prophet canceled the manumission (and sold the slave for him). Nu'aim bin Al-Nahham bought the slave from him.