Bismillah wa salatu wa salamu ala rasulallah.
Ibn Sad reported in Tabaqat al-Kabir (3/16-17, TaHa Publishers):
Yazid ibn Haroon reported from Ismail ibn Abi Khalid that ash-Shabi said: I saw Ali. He had a large beard which filled all that was between his shoulders..”.
al-Fadl ibn Dukayn reported from Yunus ibn Abi Ishaq that his father Abu ismail said: I saw Ali and my father said to me: Amr look at the commander of faithful. I went to him and I saw that he did not dye his beard. He had a large beard“.
Shihab ibn Abbad al-Abdi reported from Ibrahim ibn Humayd from Ismail that Amir said: I have never seen a man with a larger beard than Ali. It filled the space between his shoulders and was white.
al-Fadl ibn Dukayn reported that Rizam ibn Sad ad-Dabbi heard his father describing Ali, he said: A man taller than medium with large shoulders and a long beard..
gift2shias.com 
Assalamu alaikum,
Jazakallah, It is quite consistent in Ahl-Sunna’s texts but where did the shi’a get the description from that caused them to make the almost uniform picture they make of Ali (r.a)? I once heard a Muslim historian say it has been copied from a portrait of a Tunisian boy in modern times, how true is it?
Jazakallah
Ramadan Kareem
Ibn ‘Abdul-Ban (may Allah have mercy on him) said: The
best description that I have seen of ‘Ali (r.a) is that he was of average
height, if not on the short side, with wide black eyes, a handsome face
like the moon when it is full, a large belly, broad shoulders, large
hands and a neck like silver brocade. He was bald, with no hair on his
head except at the back; his beard was large and thick. The bones of
his shoulders were like the bones of a strong lion, and there was no
difference between his forearm and upper arm, as if they were one. If
he held a man’s arm, the man would not he able to breathe. Even
though he was somewhat fat, his arm and hand were very powerful.
When he walked in battle he almost ran, and he looked steadfast,
strong and brave.
(Ali Ibn Abi Talib Vol 1 p67 by Dr. Ali M. Sallabi)