Narrated Ibn 'Umar: Allah's Apostle forbade Al-Muzabana, i.e. to sell ungathered dates of one's garden for measured dried dates or fresh ungathered grapes for measured dried grapes; or standing crops for measured quantity of foodstuff. He forbade all such bargains.
— Sahih Bukhari, Volume 3, Book 34: Sales and Trade, Hadith #407
