Musnad Ahmad 32:1358

Aswad ibn Amir narrated to us, Isra'il narrated to us, from Abd al-A'la, from Bilal ibn Abi Musa, from Anas ibn Malik, who said: Al-Hajjaj wanted to appoint his son as the judge of Basra. Anas said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, say: "Whoever seeks the position of judge and seeks help for it, he is left to it. And whoever does not seek it, and does not seek help for it, Allah sends down an angel to guide him."