Musnad Ahmad 32:244

Waki’ narrated to us, Isra’il narrated to us, from ‘Abd al-A’la al-Tha’labi, from Bilal ibn Abi Musa, from Anas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever seeks the position of judge is left to himself, and whoever is forced into it, an angel descends upon him to guide him."