It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: Do not sell one dinar for two dinars, nor one dirham for two dirhams, nor one sa’ for two sa’s, for I fear that you may fall into usury. A man stood up and said,“O Messenger of Allah! What is your ruling regarding a man selling one horse for several horses, or a she-camel for a camel?”He (peace and blessings be upon him) said: When it is hand to hand, there is no harm in it.