Musnad Abu Ya'la al-Mawsili 109:208

Abdullah ibn Umar ibn Aban narrated to us, Abd al-Rahim ibn Sulayman narrated to us, Ash'ath narrated to us, from Abu al-Zubayr al-Makki, who said: I asked Jabir ibn Abdullah about wheat for dates, and the surplus, hand-to-hand. He said: We used to, during the time of the Messenger of Allah (may Allah bless him and grant him peace), buy a sa' of wheat for six sa's of dates, hand-to-hand. But if it is of the same type, then there is no good in it except like for like.