Musannaf Ibn Abi Shayba 13:2079

Abu Bakr narrated to us, he said: Ibn Fudayl narrated to us, from Hajjaj, from ‘Amr ibn Shu’ayb, from his father, from his grandfather, who said: The Prophet, may Allah bless him and grant him peace, sent ‘Attab ibn Asid to the people of Makkah. He said: "Do you know to whom I have sent you? I have sent you to the people of Allah." Then he said: "Forbid them from four things: from a sale and a loan, from two conditions in one sale, from the profit of what is not guaranteed, and from selling what you do not possess."