Ismail Shaybani says that I asked Sayyiduna Ibn Umar (may Allah be pleased with them both), "If I sell the fruit on the date palm for one hundred wasqs, so that if the fruit on the date palm turns out to be more than one hundred wasqs, it is yours, and if it is less, you are still responsible (is such a transaction permissible)?" Sayyiduna Ibn Umar (may Allah be pleased with them both) replied that the Messenger of Allah (peace and blessings be upon him) forbade selling fruit for fruit, except he permitted the sale known as 'ariyah.'
Hadith Referenceالسنن المأثورة / باب في البيوع / 194