Anas reported that the Prophet (peace and blessings of Allaah be upon him) passed by some people who were wrestling. He asked, "What is this?" They said: "So-and-so is the strongest, he can beat anybody." The Prophet (peace and blessings of Allaah be upon him) said,
"Shall I not tell you who is even stronger then him? The man who, when he is mistreated by another, controls his anger, has defeated his own shaytaan and the shaytaan of the one who made him angry."
(Reported by al-Bazzaar, and Ibn Hijr said its isnaad is saheeh. Al-Fath, 10/519)
Do not become angry and Paradise will be yours (a saheeh hadeeth, see Saheeh al-Jaami’, 7374. Ibn Hijr attributed it to al-Tabaraani, see al-Fath 4/465):
Remembering what Allaah has promised to the righteous (muttaqeen) who keep away from the causes of anger and struggle within themselves to control it, is one of the most effective ways of extinguishing the flames of anger. One of the ahaadeeth that describe the great reward for doing this is:
"Whoever controls his anger at the time when he has the means to act upon it, Allaah will fill his heart with contentment on the Day of Resurrection."