Musannaf Ibn Abi Shayba 13:2550

Abu Bakr narrated to us, he said: Ibn ‘Uyaynah narrated to us, from ‘Ubayd Allah ibn Abi Yazid, from Ibn ‘Abbas, from Usamah, he said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Verily, usury (riba) is only in the deferred exchange (nasi'ah)."