Musnad Abu Ya'la al-Mawsili 2:69

Ubayd Allah ibn Umar al-Qawariri narrated to us, Yazid ibn Zuray' narrated to us, Ma'mar narrated to us, from al-Zuhri, who said: Malik ibn Aws ibn al-Hadthan narrated to us, saying: Talhah ibn Ubayd Allah exchanged silver for gold with me. He said: "Wait for us until our produce comes from al-Ghabah." Umar ibn al-Khattab heard him and said: "No, by Allah, you shall not leave him until you pay him in full, for I heard the Messenger of Allah (ﷺ) say: 'Gold for silver is usury (riba) unless it is hand-to-hand (spot exchange), wheat for wheat is usury unless it is hand-to-hand, barley for barley is usury unless it is hand-to-hand, and dates for dates is usury unless it is hand-to-hand.'"