Malik bin Aws said: I needed to exchange one hundred dinars for dirhams, so Talha bin Ubaidullah called me. Then we both agreed on the exchange, and he took the dinars from me and began turning them over in his hand, and said: "Wait until my treasurer comes from Ghaba" (Ghaba is a place near Madinah). When Umar (may Allah be pleased with him) heard this, he said: "No, by Allah! Do not leave Talha until you have taken your money." The Messenger of Allah (peace and blessings be upon him) said: "Selling gold for silver is riba except when it is hand to hand, and selling wheat for wheat is riba except when it is hand to hand, and selling dates for dates is riba except when it is hand to hand, and selling barley for barley is riba except when it is hand to hand, and selling salt for salt is riba except when it is hand to hand."
Imam Malik, may Allah have mercy on him, said that if a person took rupees in exchange for gold coins, and then one rupee turned out to be counterfeit, and now he wishes to return it, then he should return all the gold coins, and all the rupees should be given back to him, because the Messenger of Allah, peace and blessings be upon him, said: "There is riba in exchanging gold for silver except when it is hand to hand." And Sayyiduna Umar, may Allah be pleased with him, said: If he asks you for time to go home, do not grant him respite; if you return one rupee to him and separate from him, it will become like a debt or a term, and for this reason, it is disliked. One should annul such a sale oneself, so that on one side it is cash and on the other side it is a promise, whether it is of one kind or of several kinds.
Hadith Referenceموطا امام مالك رواية يحييٰ / كتاب البيوع / 1340