Musannaf Ibn Abi Shayba 13:2964

Abu Bakr narrated to us, he said: Mu'tamir narrated to us, from his father, who said: Tawus was asked about *salam* (forward sale) in goods (*'urud*), or he said: the goods (*al-'urud*). He said: "There is no harm in it." And he was asked about *salam* in silk, and he said: "I do not know what silk is."