Musnad Ahmad 482:149

Hassan narrated to us, Ibn Lahi'ah narrated to us, Yazid ibn 'Amr al-Ma'afiri narrated to us, from someone who heard 'Uqbah ibn 'Amir saying: "The Messenger of Allah (peace and blessings of Allah be upon him) sent me as a collector [of Zakat]. I asked his permission to eat from the charity, and he gave me permission."