Musnad Ahmad 941:36

Sufyan narrated to us, from Ubayd Allah ibn Abi Yazid, who heard Ibn Abbas saying: Usamah ibn Zayd narrated to me, from the Messenger of Allah, may Allah bless him and grant him peace. And he said once: Usamah informed me, that he said: "Riba (usury) is in the Nasi'ah (deferment)."