Sahih Bukhari Volume 3, Book 34, Hadith Number 410.

Narated By Humaid : Anas said, “The Prophet forbade the selling of dates till they were almost ripe.” We asked Anas, “What does ‘almost ripe’ mean?” He replied, “They get red and yellow. The Prophet added, ‘If Allah destroyed the fruits present on the trees, what right would the seller have to take the money of his brother (somebody else)?'”