Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.031.

Section : Running one’s fingers through his beard.

‘Aishah reported that the Messenger of Allah would run his fingers through his beard. (Related by Ibn Majah and at-Tirmizhi, who classified it as sahih.)

Anas said that when the Messenger of Allah performed ablution, he would take a handful of water and put it under his jaws and pass it through his beard. He said, “This is what my Lord, Allah, ordered me to do.” (Related by Abu Dawud, al-Baihaqi and al-Hakim.)