Musnad Ahmad 1119:32

'Abd al-Rahman narrated to us, from Mu'awiyah, from Azhar ibn Sa'id, from Dhu Kala', from 'Awf ibn Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The collectors of alms (al-qassas) are three: an amir (commander/appointed collector), or one who is commanded (an agent), or a pretentious person (one who takes more than his due)."