Musannaf Ibn Abi Shayba 13:2292

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Sufyan narrated to us, from ‘Abd al-Wahid, from al-Hakam, regarding the Syrian dinar for the Kufan dinar, while the Syrian one has a surplus of silver: He said, "There is no harm in it."