Abu Hurayra reported that the Messenger of Allah, may Allah bless him and grant him peace, said, “The person who is strong is not strong because he can knock people down. The person who is strong is the one who controls himself when he is angry.”
حَدَّثَنَا إِسْمَاعِيلُ قَالَ‏:‏ حَدَّثَنِي مَالِكٌ، عَنِ ابْنِ شِهَابٍ، عَنْ سَعِيدِ بْنِ الْمُسَيِّبِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللهِ صلى الله عليه وسلم قَالَ‏:‏ لَيْسَ الشَّدِيدُ بِالصُّرَعَةِ، إِنَّمَا الشَّدِيدُ الَّذِي يَمْلِكُ نَفْسَهُ عِنْدَ الْغَضَبِ‏.‏
Reference : Al-Adab Al-Mufrad 1317
In-book reference : Book 57, Hadith 1
English translation : Book 57, Hadith 1317