Sahih Bukhari Volume 003, Book 035, Hadith Number 450.

Narated By Abu Bakhtari At-Tai : I asked Ibn 'Abbas about Salam for (the fruits of) date-palms. He replied "The Prophet forbade the sale a dates on the trees till they became fit for eating and could be weighed." A man asked what to be weighed (as the dates were still on the trees). Another man sitting beside Ibn 'Abbas replied, "Till they are cut and stored." Narrated Abu Al-Bakhtari: I heard Ibn Abbas (saying) that the Prophet forbade... etc. as above.