Musannaf Ibn Abi Shayba 1:98

98. Sufyan ibn 'Uyaynah narrated to us, from 'Abd al-Karim, from Hassan ibn Bilal, who said: I saw 'Ammar ibn Yasir perform ablution (wudu), and he combed his beard with his fingers. I said to him [regarding that], and he said: I saw the Messenger of Allah, may Allah bless him and grant him peace, do it.