Hazrat Mahdi's (as) beard will be copious and thick

His (HAZRAT MAHDI’S (AS)) beard will be copious and thick. (Ibn Hajar al-Haythami, Al-Qawl al-Mukhtasar fi `Alamat al-Mahdi al-Muntadhar, p. 23)

His [Hazrat Mahdi’s (as) beard is thick. (Al-Barzanji, Al-Isha'ah li-ashrat al-sa'ah, p. 163)

... He [Hazrat Mahdi (as)] has black hair. His beard is black. (Mari’ bin Yusuf Karami Hanbali, Fawaid Fawaid al-Fikr fil Mahdi al-Montazar)

...  The light of his [Hazrat Mahdi’s (as)] face shines like day over the blackness of his hair, beard and head, and gives him grandeur. (Al-Uqayli, An-Najmu's-saqib fi Bayan Anna'l Mahdi min Awladi Ali b. Abu Talib Ale't-Tamam wa al-Qamal)

Hazrat Mahdi (as) has a thick beard... (Mari’ bin Yusuf Karami Hanbali, Fawaid Fawaid al-Fikr fil Mahdi al-Montazar)