It is narrated from Sayyiduna Zayd bin Thabit (may Allah be pleased with him) that he said: People used to buy and sell fruit even before it had appeared, and then they would come to the Prophet (peace and blessings be upon him) with their disputes. The Prophet (peace and blessings be upon him) said: "Since you do this, then do not buy and sell fruit until its ripeness has become evident."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4771