Musannaf Ibn Abi Shayba 13:1447

Abu Bakr narrated to us, he said: Ibn Mubarak narrated to us, from Ibrahim ibn Qusayd, he said: I asked Bukayr ibn Abd Allah ibn al-Ashajj about the *salam* (forward sale) in garments. He said: It is not valid unless the patch (quality/type) is known, and such-and-such is known.