Muwatta Imam Malik (Riwayat Yahya)

Imam Malik, may Allah have mercy on him, said that for all food items or those eaten with bread, when the type is the same, any excess or deficiency is not permissible. For example, one mudd of wheat should not be sold for two mudds of wheat, nor one mudd of dates for two mudds of dates, nor one mudd of grapes for two mudds of grapes. Similarly, for other food items or those eaten with bread that are similar to these, when their type is the same, any excess or deficiency is not permissible, even if it is hand to hand. For example, if someone sells silver for silver or gold for gold, any excess or deficiency is not permissible. Rather, it is necessary for all these things that they be equal and exchanged hand to hand.