[Ruling on selling the soil of a waqf jarbah]

Answer: That is permissible, because the flood-runoffs replace the soil with soil even better—this applies to jarab (fields) that drink from torrents or from rain-runoff streams. As for fields that are not replenished by torrents and runoffs, it is not permissible to sell their soil, and it is not permissible for the buyer to purchase it; for selling their soil is corruption, and selling is not permissible except in cases in which selling a waqf itself is permissible.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2