Musnad Ahmad 28:440

Asbat ibn Muhammad narrated to us, Ibn ‘Ajlan narrated to us, from ‘Amr ibn Shu‘ayb, from his father, from his grandfather, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) forbade a loan combined with a sale, and two transactions in one transaction, and the sale of what you do not possess, and the profit on what is not guaranteed."