Musnad Ahmad 1119:5

Hammad ibn Khalid narrated to us, from Mu'awiyah ibn Salih, from Azhar—meaning Ibn Sa'id—from Dhu al-Kala', from 'Awf ibn Malik, that the Messenger of Allah, may Allah bless him and grant him peace, used to say: "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)."