Sahih Muslim
The Book of Transactions (Kitab Al-Buyu)
Book Number: 010 / Hadith Number: 3907
Ibn 'Abbas (Allah be pleased with them) reported that when Allah's Messenger (may peace be upon him) came to (Medina) and the people were paying in advance (for the fruits, etc.), he said to them: He who makes an advance payment should not make advance payment except for a specified measure and weight (and for a specified period).