Musannaf Ibn Abi Shayba 13:523

Abu Bakr narrated to us, he said: Ibn ‘Ulayyah narrated to us, from Ayyub, from ‘Ikrimah, that he used to dislike *as-salaf* (forward sales), except for something for which he had its origin (i.e., the goods were already in his possession or guaranteed). Ayyub said: I was informed of the like of that from Tawus.