Musannaf Ibn Abi Shayba 35:410

Ibn ‘Uyaynah narrated to us, from ‘Abd al-Karim, from Hassan ibn Bilal, who said: I saw ‘Ammar ibn Yasir perform ablution and he combed his beard with his fingers. I asked him [about it], and he said: I saw the Prophet, may Allah bless him and grant him peace, do it.