It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them) that the Messenger of Allah (peace and blessings be upon him) forbade the buying and selling of fruit before its ripeness becomes apparent.
Hadith Referenceالسنن المأثورة / باب في البيوع / 188
Hadith Takhrijصحیح بخاری، الزكاة، باب من باع ثمارة او نخله ..... الخ، رقم : 1486 ۔