The very first harm of anger is that your right thinking comes to a halt.  I thought about various incidents from history. The moment anger comes, right thinking goes away. A verse from the Quran tells us that if a prophet gets angry, then even his right thinking comes to a halt. An example is the Prophet Yunus. Prophet Yunus was sent to convey God's message to the town of Nainva in Iraq. In those times, Nainva was the central city in Iraq. Prophet Yunus conveyed God's message to people there. But soon he left the place in anger.  The Quran says: وَذَا النُّونِ إِذْ ذَهَبَ مُغَاضِبًا فَظَنَّ أَنْ لَنْ نَقْدِرَ عَلَيْهِ (21:87) He left the city in anger. God Almighty was displeased with this act. Prophet Yunus then was swallowed by a whale. He later asked God for forgiveness, returned to Nainca to continue to convey God's message to people.

What was the loss incurred due to anger? When Prophet Yunus became angry, his right thinking in the matter came to a halt.  Right thinking in the matter was that it is not permissible for a prophet to leave his people unless he has given them all arguments on behalf of God's religion. The prophet cannot do this, even if people throw stones at him. Yunus was a prophet. The people of Nainva were his contemporaries and so he had no option but to live among them, regardless of their good or bad behaviour and acceptance or rejection of his message. In the matter of completing arguments on behalf of God, we cannot decide on our own.

This is something that God's angel comes to inform the prophet. He instructs the prophet to leave his city. The matter of fully conveying God's message is not something that a prophet can decide based on his own reasoning. This is why, after the prophets, no Muslim individual or group has the right to say that they have presented all arguments on behalf of God to people. They cannot make this statement. We can only convey God's message to people. We have to die in this state. No angel is going to come and tell us that we have fulfilled our responsibility with regard to conveying God's religion. It would be sheer arrogance to leave a city or its people, saying we have fully conveyed God's religion to them. No person, after the prophets, has the right to say this. People of later generations have to only convey God's message. This is the state in which they must die. No angel is going to come to tell us that we have fully conveyed God's religion to people. Prophet Yunus decided himself that he had fulfilled his duty toward conveying God's religion. No angel had come to tell this to him. This is why, he had to return to Nainva.

This example shows that if a prophet gets angry, that affects his divine wisdom. He won't have right thinking and thus would take wrong decisions. This is the final example to awaken us. The prophet too is no exception in this matter. When a prophet gets angry, even his right thinking comes to a halt. How can we then save ourselves from anger? This is a very serious matter.