Musannaf Ibn Abi Shayba 20:66

Abu al-Ahwas narrated to us, from Abu Ishaq, from al-Najrani, who said: I said to Abdullah ibn Umar, "Should I make a salam (forward sale) in palm trees before they sprout?" He said, "No." I said, "Why?" He said, "A man made a salam during the time of the Messenger of Allah (peace and blessings of Allah be upon him) for a garden of palm trees before they sprouted, and they did not produce anything that year. The buyer said, 'It is mine until they sprout,' and the seller said, 'I only sold you the palm trees of this year.' They disputed before the Messenger of Allah (peace and blessings of Allah be upon him)." The Messenger of Allah (peace and blessings of Allah be upon him) said to the seller, "Did you take anything from his palm trees?" He said, "No." The Messenger of Allah (peace and blessings of Allah be upon him) said, "Then by what right do you deem his wealth lawful? Return to him what you took from him, and do not make a salam in palm trees until their ripeness becomes apparent."