Sahih Bukhari
Sahih Bukhari Volume 003, Book 035, Hadith Number 445.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 35. Sales in Which a Price is paid for Goods to be Delivered later (As-Salam)
Narated By Ibn 'Abbas : The Prophet came (to Medina) and he told the people (regarding the payment of money in advance that they should pay it) for a known specified measure and a known specified weight and a known specified period.