What is the reason for the revelation of Allah's saying: "And among the people is he who sells himself, seeking the pleasure of Allah; and Allah is full of kindness to [His] servants"?

The exegetes differed regarding whom the verse was revealed about. Some said: it was revealed about Suhayb when he emigrated and left his wealth behind for the disbelievers of Mecca. Others said: it was revealed about whoever plunges into the enemy ranks and is killed. And still others said: it was revealed about whoever enjoins good and forbids evil.