Anger is a psychological state that results from inner agitation and desire for vengeance. And when this agitation becomes more violent, it intensifies the fire of anger. A violent commotion engulfs ones brain on account of which, the mind and the intellect lose control and become powerless. At that time, the inner state of the person resembles a cave where fire has broken out, filling it with flames and suffocating clouds of smoke that leap out of its mouth with intense heat and a fiery howl. When that happens, it becomes extremely difficult to pacify such a person and to extinguish the fire of his wrath; whatever is thrown in it to cool it down becomes a part of it, adding to its intensity. It is for this reason that such a person becomes blinded to etiquette and deaf to guidance. In such a condition, all such efforts as counsel, advice, and exhortation fail to appease him. The more one tries to pacify him through humble entreaties and tearful supplications, the more violent he becomes until the angry person physically harms someone or seeks revenge.
Imam Baqir (A.S) said: “Indeed, this anger is the spark lit by Satan in the heart of the son of Adam..” [Al-Kulayni, al-Kafi, vol. 2, p. 304, hadith # 12]
Imam Ja’far Sadiq (A.S) said: “Anger is the key (that opens the door) to all kinds of vices.” [Al-Kulayni, al-Kafi,vol. 2, p. 303, hadith # 3]
It is narrated from Imam Sadiq (A.S) that he heard his father Imam Baqir (A.S), as saying: “A Bedouin came to the Prophet (pbuh&hh) and said: ‘I live in the desert. Teach me the essence of wisdom.’ Thereupon the Prophet (pbuh&hh) said to him: ‘I command you not to get angry’. After repeating his question thrice (and hearing the same reply from the Prophet (pbuh&hh) every time) the Bedouin said to himself: ‘After this I will not ask any question, since the Apostle of God (pbuh&hh) does not command anything but good’.” Imam Sadiq (A.S) says: “My father used to say, ‘Is there anything more violent than anger? Verily, a man gets angry and kills someone whose blood has been forbidden by God, or slanders a married woman’.” [Al-Kulayni, al-Kafi, vol. 2, p. 303, hadith # 4]
Imam Ja’far Ibn Mohammad Sadiq (A.S) has stated that “Anger spoils faith just as vinegar spoils honey.”
source:english.almaaref