He said it out loud

Abu Dharr had come a long way on a rumour, spent days in Makkah without being able to ask anyone a direct question, and finally found the man he was looking for. He accepted Islam.

The advice he was given was practical: go back to your people, keep this to yourself, and wait until you hear that we have come out into the open.

His reply was that by the One in whose hand is my soul, I will shout it among them.

He went to the gathering at the Ka'bah and announced it.

They set on him and beat him until he was on the ground. What saved him was a piece of information: al-Abbas leaned over him and told the crowd that this man was from Ghifar — and that their trade road to Syria ran through Ghifar's territory. They let him go.

The reports have him doing the same thing again the next day, with the same result and the same rescue.

It is worth noticing that he was not brave in a vacuum. He was brave and he was also, twice, spared by a commercial calculation somebody else made on his behalf. The sources keep both halves.

The account is in both Sahih collections, narrated at length by Abu Dharr himself.