Musannaf Ibn Abi Shayba 13:2545

Abu Bakr narrated to us, he said: Mu'tamir ibn Sulayman narrated to us, he said: I heard Abd al-Aziz ibn Hakim saying: I witnessed Ibn Umar, and a man from the people of Basra came to him and said: "I have come from a people who exchange small dirhams and take large ones for them." He said: "Do they increase [in quantity]?" He said: "Yes." He said: "No, unless it is weight for weight."