(1) The Book of Purification and its Sunnah
كتاب الطهارة وسننها
(50) Chapter: Concerning running the fingers through the beard (when performing ablution)
(50) باب مَا جَاءَ فِي تَخْلِيلِ اللِّحْيَةِ
Sunan Ibn Majah 432 
It was narrated that Ibn 'Umar said:
"Whenever the Messenger of Allah performed ablution, he rubbed the sides of his face then run his fingers through his beard from beneath."
حَدَّثَنَا هِشَامُ بْنُ عَمَّارٍ، حَدَّثَنَا عَبْدُ الْحَمِيدِ بْنُ حَبِيبٍ، حَدَّثَنَا الأَوْزَاعِيُّ، حَدَّثَنَا عَبْدُ الْوَاحِدِ بْنُ قَيْسٍ، حَدَّثَنِي نَافِعٌ، عَنِ ابْنِ عُمَرَ، قَالَ كَانَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ إِذَا تَوَضَّأَ عَرَكَ عَارِضَيْهِ بَعْضَ الْعَرْكِ ثُمَّ شَبَكَ لِحْيَتَهُ بِأَصَابِعِهِ مِنْ تَحْتِهَا ‏.‏
Grade :  Da'if (Darussalam)
Reference : Sunan Ibn Majah 432
In-book reference : Book 1, Hadith 166
English translation : Vol. 1, Book 1, Hadith 432