Musnad Ahmad 799:29

Hassan ibn Musa narrated to us, Shayban ibn Abd al-Rahman narrated to us, from Abd al-Malik, from Zayd ibn Uqbah al-Fazari, who said: I entered upon al-Hajjaj ibn Yusuf and said: "May Allah rectify the Amir, shall I not narrate to you a hadith that Samurah ibn Jundab narrated to me from the Messenger of Allah, peace and blessings of Allah be upon him?" He said: "Yes." He said: I heard him saying: The Messenger of Allah, peace and blessings of Allah be upon him, said: "Asking (for charity) is a scratching with which a man scratches his own face. So, whoever wishes may leave (some skin) upon his face, and whoever wishes may leave it (i.e., stop asking). Except if a man asks someone in authority, or asks regarding a matter that is unavoidable."