It is narrated from Sayyiduna Abu Hurairah, may Allah be pleased with him, that the Messenger of Allah, peace and blessings be upon him, said: Wheat for wheat, barley for barley, dates for dates, and salt for salt shall be sold by measure and equally. Whoever gives more or demands more, he will have taken usury. However, when the types differ, then there is no harm in giving or taking more.