Sayyiduna Umar bin Khattab (may Allah be pleased with him) said: Do not sell gold for gold except equal for equal, do not increase one over the other, and do not sell silver for silver except equal for equal, do not increase one over the other, and do not sell silver for gold in such a way that one is immediate and the other is deferred, rather, if he asks you for so much respite that he may go to his house and return, do not even permit that much, I fear usury for you.