Ibn `Abbas reported that when Abu Dharr heard of the advent of the Apostle (ﷺ) in Mecca he said

Brother, ride in this valley and bring information for me about the person who claims that there comes to him information from the Heavens. Listen to his words and then come to me. So he rode on until he came to Mecca and he heard his words (the sacred words of the Holy Prophet ) and then came back to Abu Dharr and said: I have seen him exhorting (people) to develop good morals and his expressions can in no way be termed as poetry. He (Abu Dharr) said: I have not been satisfied with it regarding that which I had in my mind (as I sent you). So he took up provisions for the journey and a small water-skin containing water (and set forth) until he came to Mecca. He came to the mosque (Ka`bah) and began to look for Allah's Messenger (ﷺ) and he did not recognize him (the Holy Prophet) and he did not even like that he should ask about him from anyone until it was night, and he slept. `Ali saw him and found him to be a stranger. So he went with him. He followed him but one did not make any inquiry from the other about anything until it was morning. He then brought the water and his provisions to the mosque and spent a day there, but he did not see Allah's Messenger (ﷺ) until it was night. He then returned to his bed, and there happened to pass `Ali and he said: This man has not been able to find his destination until this time. He made him stand and he went with him and no one made an inquiry from his companion about anything. And when it was the third day he did the same. `Ali made him stand up and brought him along with him. He said: By Him, besides Whom there is no god, why don't you tell me (the reason) which brought you here to this town? He said: (I shall do this) provided you hold me promise and a covenant that you would guide me aright. He then did that. He (`Ali) said: Verily, he is truthful and he is a Messenger of Allah (ﷺ) and when it is morning, follow me and if I would say anything from which I would sense fear about you I would stand (in a manner) as if I was throwing water and if I move on, you then follow me until I get in (some house). He did that and I followed him until he came to Allah's Messenger (ﷺ). He entered (the house) of Allah's Messenger (ﷺ) along with him and listened to his words and embraced Islam at this very place. Allah's Messenger (ﷺ) said to him: Go to your people and inform them until my command reaches you. Thereupon he said: By Him in Whose Hand is my life, I shall say to the people of Mecca this thing at the top of my voice. So he set forth until he came to the mosque and then spoke at the top of his voice (saying): I bear testimony to the fact that there is no god but Allah and that Muhammad is the Messenger of Allah. The people attacked him and made him fall down when al-`Abbas came and he leaned over him and said: Woe be upon you, don't you know that he is from amongst the tribe of Ghifar and your trading route to Syria passes through (the settlements of this tribe), and he rescued him. He (Abu Dharr) did the same on the next day and they (the Meccans) again attacked him and al-`Abbas leaned upon him and he rescued him.