Salim bin Abdullah narrates from his father (Sayyiduna Abdullah bin Umar (may Allah be pleased with them both)) that the Messenger of Allah (peace and blessings be upon him) "forbade selling fruits before they ripen."
Al-Zuhri (may Allah have mercy on him) said: The scholars say that (its ripening is) that it turns yellow, and the ripening of crops is that the ear becomes fit to be rubbed out.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10616