Musannaf Ibn Abi Shayba 13:2538

Abu Bakr narrated to us, he said: Ibn Fudayl narrated to us, from Layth, from Mujahid, who said: Fourteen of the companions of Muhammad, may Allah bless him and grant him peace, said: "Gold for gold, and silver for silver, and they considered the surplus (al-fadl) to be usury (riba)." Among them were Abu Bakr, Umar, Uthman, Ali, Sa'd, Talha, and al-Zubayr.