Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) says that the Messenger of Allah (peace and blessings be upon him) forbade selling the fruit of date palms before it ripens. Ibn Umar (may Allah be pleased with them both) says: Its ripening is that it can be eaten from.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10590