Sahih Bukhari
Sales in which a Price is paid for Goods to be Delivered Later (As-Salam)
Volume: 003 / Book Number: 035 / Hadith Number: 455
Narrated Ibn 'Abbas:
The Prophet came to Medina and the people used to pay in advance the prices of fruits to be delivered within two to three years. The Prophet said (to them), "Buy fruits by paying their prices in advance on condition that the fruits are to be delivered to you according to a fixed specified measure within a fixed specified period." Ibn Najih said, " ... by specified measure and specified weight."