Malik bin Aws bin Hadthan (may Allah be pleased with him) says: I came (to the market) saying: Who will exchange dirhams (for dinars, etc.)? So Talhah bin Ubaidullah (may Allah be pleased with him) said, and he was with Umar bin Khattab (may Allah be pleased with him): Show us your gold, and when our servant comes, come to us and we will give you silver in exchange for it. (Upon hearing this) Umar (may Allah be pleased with him) said: By Allah! This can never be. Either give him the silver right now or return his gold, because the Messenger of Allah (peace and blessings of Allah be upon him) said: "Exchanging gold for silver is usury, except when it is hand to hand; exchanging wheat for wheat is usury, except when it is hand to hand; exchanging barley for barley is usury, except when it is hand to hand; and exchanging dates for dates is usury, except when it is hand to hand." Imam Tirmidhi says:
1- This hadith is Hasan Sahih,
2- The people of knowledge act upon this.
«إلاھاء وھاء» means immediate exchange.