Musnad Abu Ya'la al-Mawsili 108:112

Abdullah ibn Umar ibn Aban narrated to us, Abd al-Rahim ibn Sulayman narrated to us, al-Hajjaj ibn Artah narrated to us, from Ata ibn Abi Rabah and Abu al-Zubayr al-Makki, from Jabir ibn Abdullah al-Ansari: That the Messenger of Allah (may Allah bless him and grant him peace) forbade that palm trees be sold for two or three years. And he forbade that what is in the tops of the palm trees be bought with a measured amount of dates. And he forbade that fruit be sold until its ripeness becomes apparent.