Musnad Ahmad 25:307

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Ayyub, from Sa'id ibn Jubayr, from Ibn Abbas, from the Prophet, may Allah bless him and grant him peace, that he said: "In the *salaf* (forward sale) of the *habal al-habalah* (the offspring of the offspring), there is *riba* (usury)."