Musannaf Ibn Abi Shayba 13:494

Abu Bakr narrated to us, he said: Yahya bin Zakariya bin Abi Za'idah narrated to us, from Ash'ath, from 'Ikrimah, from Ibn 'Abbas, he said: "There is no harm in saying regarding a commodity: 'It is for such-and-such price in cash, and for such-and-such price on credit,' provided they do not part ways except upon mutual agreement."