´Hassan bin Bilal said:` "1 saw Ammar bin Yasir performing Wudu, so he went through his beard (with his hand). It was said to him" - or he said - "1 said: 'You go through your beard?' He said: 'And what is there to prevent me? Indeed I saw Allah's Messenger going through his beard.'"
Explanation & Benefits
Shaykh Dr. Abdur Rahman Freywai
1:
From this hadith, it is understood that passing the fingers through the beard (khilal) is Sunnah. Some people hold the view that it is obligatory (wajib), but upon examining all the evidences, it is established that it is Sunnah and not obligatory. This is the opinion of the majority (jumhur).
Source: Sunan al-Tirmidhi – Majlis ‘Ilmi Dar al-Da‘wah, New Delhi Edition, Page: 29