Sahih Bukhari Volume 003, Book 035, Hadith Number 452.
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 Abu Al-Bakhtari : I asked Ibn 'Umar about Salam for dates. Ibn 'Umar replied, "The Prophet forbade the sale (the fruits) of datepalms until they were fit for eating and also forbade the sale of silver for gold on credit." I also asked Ibn 'Abbas about it. Ibn 'Abbas replied, "The Prophet forbade the sale of dates till they were fit for eating, and could be weighed." I asked him, "What is to be weighed (as the dates are on the trees)?" A man sitting by Ibn 'Abbas said, "It means till they are cut and stored."