He was known for being an ascetic, intelligent, knowledgeable, correctness of Madhab (school of thought), living in minimum and giving up what was more than needed. He was very cautious when narrating Prophetic Narrations, fearing to narrate something which maybe weak or fabricated. This is why he said:
"No one should ever narrate a Hadith until he is sure it is authentic."
He was companion and friend of Imaam Ahmad ibn Hanbal. That's why we find 'Abdullah ibn Ahmad narrate that when Bishr passed away, '...I advised my father, Imam Ahmad, about his death so my father said:
"May Allah bestows his mercy upon him, we always enjoyed his remembrance."
Then he left and witnessed his funeral.' Furthermore, Ibn Hibbaan said in his book "Ath-Thiqaat":
'Bishr was following the Madhab of Sufyaan Ath-Thawri in his Madhab.'
This proves that he was not a Sufi heretic.
It was said that he used to be a thief and one day he found a piece of paper with the name of Allah Almighty on it, thrown in a dirty place. He became upset, picked up the paper and cleaned it. He only had one Dirham and with that he purchased perfume. He perfumed this paper and placed it on a wall.
After this incident he went to visit his friend. His friend informed him of a dream he had seen, the like of which he had never seen in his life and said to Bishr,
'I will not tell you the dream until you tell me about something you did in secret and which only you and Allah know about.'
Bishr replied: 'I do not recall anything but…( he mentioned his story of paper).'
The man told him his dream and said 'Someone called out to me and said:
"Tell Bishr you raised our name to glorfy it and we will raise your name in this life and hereafter."
Source: Tahtheeb At-Tahtheeb by Ibn hajar and Tahtheeb Al-Kamaal by Al-Mizzi and Ath-Thiqaat by Ibn Hibbaan.