“Abu ‘Abd Allah (a.s.), has said, ‘It is not permissible to sell two Makhtum (a container) of barley for one Makhtum of wheat. These items cannot be exchanged except in equal quantities of each other and so also is the date.’ Abu ‘Abd Allah (a.s.), was asked about the case of a man who buys wheat but cannot find with his party anything except barley, if he can take two for one. He (the Imam) said, ‘No, because the origin of the two is the same and Ali (a.s.), would count barley for wheat.’”