Sayyiduna Anas (may Allah be pleased with him) says that the Prophet (peace and blessings be upon him) forbade selling the fruit of date palms before it ripens. I said to Sayyiduna Anas (may Allah be pleased with him): What is its ripening? He said: Turning red and yellow. He (peace and blessings be upon him) says: "If Allah Almighty withholds the fruit, then how will you consider your brother's wealth lawful?"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10596