Shaykh Abdul Muhsin al-Abbaad حفظه الله said, “Running wet fingers inside the beard is preferable. What is obligatory is to wash the front part of beard which faces others.”
[Taken from the lessons on “Conditions, Pillars and Obligation of Salah – Shaykh ul Islaam Muhammad bin Abdil Wahhab رحمه الله Explanation by Shaykh Abdul Muhsin al-Abbaad حفظه الله Taught by: Abdulilah Lahmami]