Abu Al-Ash'ath (may Allah be pleased with him) says that people used to sell the silver obtained from war booty by suspending it until they received their stipend. Seeing this, Hazrat Ubadah (may Allah be pleased with him) said that the Noble Prophet (peace and blessings be upon him) forbade the exchange of gold for gold, silver for silver, dates for dates, wheat for wheat, barley for barley, and salt for salt, except when it is equal for equal. Whoever adds or asks for an addition has engaged in usury.