Musannaf Ibn Abi Shayba 13:2296

Abu Bakr narrated to us, he said: Jarir narrated to us, from Mughira, from Ibrahim, who said: It is disliked to exchange a Levantine dinar for a Kufan dinar and a dirham. There is no harm if you have a claim of a Kufan dinar against a man, that you give him a Levantine dinar and purchase the surplus from him with something, provided you do not separate until what is between you has been settled.