I say, and with God's success: Whoever extracted wheat from wheat based on value, by giving half a sa' of good wheat for a sa' of average wheat, for example, it is not permissible; because it is not permissible to perform what is specified partially for another based on value, whether the one performed is of the same kind or of a different kind after it has been specified. Value is only considered in what is not specified. Refer to: Bada'i al-Sanai' 2: 72/73, and God knows best.