While this is a concept mentioned by Hadrat Shaykh Mawlana Zakariyyah saheb in his booklet on the beard and perpetuated by most of our Ulama, even by some Muhaqqiqin like Mf. Rashid Ahmed Ludyanwi saheb, I have never been able to understand it with regard to the beard. (Edit: It seems that this concept wasn't mentioned by Hadrat Shaykh, rather by other Ulama)