Musnad Ahmad 941:21

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, 'Ubayd Allah ibn 'Ali ibn Abi Rafi' narrated to me, from Sa'id ibn al-Musayyib, Usamah ibn Zayd narrated to me, that he heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "There is no usury (riba) except in the deferred (al-nasi'ah)."