Hmam bin Yahya bin Dinar همام بن يحيى بن دينار · Commercial Transactions (Kitab Al-Buyu)

The Messenger of Allah (ﷺ) as saying: Gold for gold is interest unless both hand over on the spot ; wheat for wheat is interest unless both hand over on the spot ; dates for dates is interest unless both hand over on the spot ; barley for barley is interest unless both hand over on the spot.