Musnad Ahmad 572:21

Abu Ahmad al-Zubayri narrated to us, Abdullah—meaning Ibn Abd al-Rahman ibn Ya'la al-Ta'ifi—narrated to us, from Abdullah ibn al-Hakam, that he heard Uthman ibn Abi al-As saying: The Messenger of Allah, peace and blessings of Allah be upon him, appointed me over al-Ta'if. The last thing the Messenger of Allah, peace and blessings of Allah be upon him, enjoined upon me was that he said: "Lighten the prayer for the people."