Musnad Abu Ya'la al-Mawsili 105:3

Harun ibn Ma'ruf and Abu Khaythama narrated to us, they said: Sufyan narrated to us, from 'Abd al-Karim Abu Umayya, that Hassan ibn Bilal al-Muzani narrated to him that he saw 'Ammar ibn Yasir perform ablution (wudu'), and that he combed his beard with his fingers. It was said to him: "Do you do this?" He said: "I saw the Messenger of Allah, may Allah bless him and grant him peace, do it."