Musannaf Ibn Abi Shayba 13:2941

Abu Bakr narrated to us, he said: Abd al-Salam narrated to us, from Ishaq ibn Abdullah—meaning Ibn Abi Farwa—from Ghaylan, he said: I said to Umar ibn Abd al-Aziz: "If only you would change these dirhams, for they fall into the hands of the Jew, the Christian, the ritually impure person, and the Magian." He said: "Do you want the nations to argue against us?" He said: "Do you want to change a monotheistic statement (Tawhid) that is among us while they are among us?"