There is a very well-known story about the ikhlas of Hazrat Ali (Radhiallaho Anho). Once, while fighting with a non-believer, he overpowered him and was sitting on
top of him ready to deliver the final blow with his sword.
At that moment, the non-believer spat on his face. This act of the disbeliever made Hazrat Ali (Radhiallaho Anho) feel very much displeased. In spite of this, he placed his sword back into its sheath and got off from him. In other words, he immediately refrained from killing him, although he had full opportunity to do so.
As he separated himself from the enemy, the disbeliever shouted at him: “O Ameer-ul-Mumineen! What is this? After I insulted you by spitting on your face, you should have killed me immediately. You had me at your mercy and completely subdued and subjugated. What is it that stopped you from killing me?”
Hazrat Ali replied: “I had the intention of killing you solely for the pleasure of Allah Ta’ala. When you spat in my face, you stirred up my anger. If I had killed you then, this act of mine would have been out of anger of my Nafs and not out of sincerity to Allah Ta’ala. Allah Ta’ala does not accept any deed which is not done out of sincerity. Killing you at that time would have been against sincerity. Hence, I refrained myself”.
Hearing these words of Hazrat Ali (Radhiallaho Anho), the enemy was astonished and the light of Imaan was lit in his heart: “I consider it my good fortune to accept such a Deen, O Ameerul-Mumineen, where such a teaching of sincerity is expounded. This Deen is undoubtedly the true Deen”.
Such it is that as a result of the action of Hazrat Ali (Radhiallaho Anho), a non-believer was blessed with iman.