Sahih Muslim Book 010, Hadith Number 3666.
Chapter : Prohibition of the sale of fruits until they are clearly in good condition.
Ibn 'Umar (Allah be pleased with them) reported that Allah's Messenger (may peace be upon him) forbade the sale of palm-trees (i.e. their trusts) until the dates began to ripen, and ears of corn until they were white and were safe from blight. He forbade the seller and the buyer.