Musannaf Ibn Abi Shayba 13:642

Abu Bakr narrated to us, he said: Yazid bin Harun narrated to us, from Ibn Abi Arubah, from Qatadah, from Muslim bin Yasar, from Abu al-Ash'ath al-San'ani, that Ubadah bin al-Samit said: There is no harm in selling wheat for barley, even if the barley is more, hand-to-hand. But it is not permissible on credit.