Musnad Abu Ya'la al-Mawsili 154:86

Ibrahim ibn al-Hajjaj al-Sami narrated to us, Sakin narrated to us, Abd al-Mu'min narrated to us, from Ibn Umar, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Gold for gold, silver for silver, wheat for wheat, barley for barley, salt for salt, and dates for dates, like for like, measure for measure. Whoever increases or seeks an increase has committed usury (riba)."