Abû Hurayrah relates that a man said to the Prophet (peace be upon him): “Counsel me.” The Prophet (peace be upon him) said: “Do not get angry.” The man repeated his request many times, but the Prophet (peace be upon him) kept saying: “Do not get angry.” [ Sahîh al-Bukhârî ]
The importance of this hadith:
The secret behind this hadīth's importance lies in the fact that the Prophet (peace be upon him) limited his counsel to this person in one short instruction: “Do not get angry.” Al-Nawawî informs us that Abû Muhammad `Abd Allah b. Abî Zayd said: “Everything that constitutes good manners can be derived from four hadith…” and mentioned among them the Prophet's statement “…to the one to whom he limited his counsel with: ‘Do not get angry'.”
This statement, given in this context, is rich in meaning. First, by limiting his counsel to this one short instruction, the Prophet (peace be upon us) indicates the importance of controlling one's anger, and that doing so has far-reaching implications for a person's welfare both in the worldly life and in the Hereafter.