Tawus (may Allah have mercy on him) heard Ibn Umar (may Allah be pleased with them both) saying: "Fruits should not be sold before they ripen."
(b) Ibn Abbas (may Allah be pleased with them both) says: "Fruit should not be sold until it can be eaten."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10606