Mukhtasar Muslim

‘Sayyiduna ‘Ubada bin Samit (may Allah be pleased with him) narrates that’ the Messenger of Allah (peace and blessings be upon him) said: Gold for gold, silver for silver, wheat for wheat, barley for barley, dates for dates, and salt for salt—must be equal in amount, exactly, and hand to hand (then it is permissible). But when the types differ (for example, wheat for barley), then sell as you wish (with increase or decrease), but it must be hand to hand.