He then took his journey-food and carried a waterskin of his, containing some water till be reached Mecca. He went to the Mosque and searched for the Prophet and though he did not know him, he hated to ask anybody about him. When a part of the night had passed away, `Ali saw him and knew that he was a stranger. So when Abu Dhar saw `Ali, he followed him, and none of them asked his companion about anything, and when it was dawn, Abu Dhar took his journey food and his water-skin to the Mosque and stayed there all the day long without being perceived by the Prophet, and when it was evening, he came back to his retiring place. `Ali passed by him and said, "Has the man not known his dwelling place yet?" So `Ali awakened him and took him with him and none of them spoke to the other about anything. When it was the third day. `Ali did the same and Abu Dhar stayed with him. Then `Ali said "Will you tell me what has brought you here?" Abu Dhar said, "If you give me a firm promise that you will guide me, then I will tell you." `Ali promised him, and he informed `Ali about the matter. 

`Ali said, "It is true, and he is the Messenger of Allah. Next morning when you get up, accompany me, and if I see any danger for you, I will stop as if to pass water, but if I go on, follow me and enter the place which I will enter." Abu Dhar did so, and followed `Ali till he entered the place of the Prophet, and Abu Dhar went in with him, 

The People got up and beat him painfully. Then Al-Abbas came and knelt over him ((to protect him) and said (to the people), "Woe to you! Don't you know that this man belongs to the tribe of Ghifar and your trade to Sha'm is through their way?" So he rescued him from them. Abu Dhar again did the same the next day. They beat him and took vengeance on him and again Al-Abbas knelt over him (to protect him).

Reference : Sahih al-Bukhari 3861
alternative narration: Sahih al-Bukhari 3522

He was known for his courage, his calmness and his far-sightedness and the repugnance he felt against the idols which his people worshipped. After Islam, Abu Dharr became known for his righteousness and strict Zuhd (asceticism or abstaining from the love of material wealth). 

Throughout his life, Abu Dharr narrated numerous important hadith from Rasulullah saw. Abu Dharr fought in the Battle of Uhud and migrated with his tribe to Madina from Mecca during the Hijrah. After the death of the Prophet, Abu Dharr left for the Syrian desert and stayed there during the caliphate of Abu Bakr and Umar.  

Once a man visited him and began looking at the contents of his house but found it quite bare. He asked Abu Dharr:
"Where are your possessions?"

"We have a house yonder (meaning the Hereafter)," said Abu Dharr, "to which we send the best of our possessions."

The man understood what he meant and said:
"But you must have some possessions so long as you are in this abode."

"The owner of this abode will not leave us in it," replied Abu Dharr.

Abu Dharr persisted in his simple and frugal life to the end. Once the amir of Syria sent three hundred dinars to Abu Dharr to meet his needs. He returned the money saying, "Does not the amir of Syria find a servant more deserving of it than I?" "

- "Companions of The Prophet", Vol. 1 
By: Abdul Wahid Hamid.

Main takeaways:
- Detach yourself from the love and material of wealth in Dunya, as life in this world is only temporary
- Strive hard in Dunya and have faith that Allah will reward you with only the best in Akhirah
- Stay firm to your beliefs

Abu Dharr reported that Allah's Messenger (ﷺ) said:

There is no believing servant who supplicates for his brother behind his back (in his absence) that the Angels do not say: The same be for you too. Reference : Sahih Muslim 2732 a