Musannaf Ibn Abi Shayba 13:1025

Abu Bakr narrated to us, he said: Ghundar narrated to us, from Hisham al-Dastawa'i, from Yahya ibn Abi Kathir, from 'Ata', who said: He did not see any harm in the earnings of the cupper (hajjām) by the two arbiters (al-hakamayn).