Is it valid to rent agricultural land for an unspecified share of its future yield (e.g., half or a third)?

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The established position from Ahmad is that this is not valid. This is also the opinion of the majority of the companions (Ashab). The reasoning is that the hadiths prohibiting renting for a share have no counter-evidence. Furthermore, it is a lease contract with an unknown consideration, thus invalid, similar to leasing it for a third of the yield of another piece of land. It is also leasing a tangible asset for some of its future growth, which is invalid like other assets, and there is no explicit text permitting it.