What is the explanation of the hadith, "Whoever's beard exceeds the grasp, his foolishness increases," found in Al-Tabarani's dictionary, what is the extent of its weakness, and can it be used as evidence?

It has not been reported from the Prophet (peace be upon him) that the length of the beard is an indication of a lack of intellect. Rather, a very weak hadith (definition) has been narrated with a similar meaning. Moreover, inferring a man's intellect merely from the length of his beard is without merit. It is a corrupt statement to claim that the longer a man's beard grows beyond a fist-length, the more foolish he becomes. Indeed, Abu Hanifa saw Alqamah ibn Marthad, who had a long beard and abundant intellect.