Musannaf Ibn Abi Shayba 13:2351

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Sufyan narrated to us, from Alqamah ibn Marthad, from Razin ibn Sulayman al-Ahmari, from Sa’id ibn al-Musayyib, that he said regarding the *salam* (forward sale): Do not delay it for him so that he may increase [the price] for you, and do not hasten it for him so that he may reduce [the price] for you.