Ismail Shaybani reported,

I sold the fruit on the tops of my palm trees for one hundred wasqs, with the agreement that if it exceeded that amount, the surplus would be theirs, and if it fell short, the loss would be theirs. I asked Ibn Umar about this, and he said, "The Messenger of Allah ﷺ forbade such a transaction, but he permitted it in the case of araya sales."

حدثنا سفيان عن عمرو

عن إسماعيل الشيباني

بعت ما في رءوس نخلي بمائة وسق إن زاد فلهم وإن نقص فلهم فسألت ابن عمر فقال نهى عنه رسول الله ﷺ ورخص في العرايا