Musnad Ahmad 27:612

He said: I found in my father’s book: Yazid narrated to us, he said: Shu’bah informed us, from Zayd ibn Jubayr, who said: A man asked Ibn ‘Umar about the selling of date palms. He said: "The Messenger of Allah (may Allah bless him and grant him peace) forbade the selling of date palms until their ripeness becomes apparent."