Musnad Abu Ya'la al-Mawsili 148:19

Abu Talib Abd al-Jabbar ibn Asim narrated to us, Abu al-Malih al-Raqqi narrated to us, from al-Walid ibn Zurwan, from Anas ibn Malik, who said: I performed wudu for the Messenger of Allah (may Allah bless him and grant him peace). When he washed his face, he took a handful of water and combed his beard with it from its underside. He said: "Thus did my Lord, Blessed and Exalted is He, command me."