Arabic text
عن أبي هريرة رضي الله عنه أن رسول الله صلى الله عليه وسلم قال: «لَيْسَ الشَّدِيدُ بِالصُّرَعَةِ، إِنَّمَا الشَّدِيدُ الَّذِي يَمْلِكُ نَفْسَهُ عِنْدَ الْغَضَبِ».
Translation
Abu Hurayrah (may Allah be pleased with him) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) said: "The strong man is not the one who can overpower others; rather, the strong man is the one who controls himself when he is angry."
Explanation
The Prophet (may Allah's peace and blessings be upon him) points out that true strength is not the strength of a person's body or his ability to overpower other strong men. But a truly strong person is one who strives to control and restrain himself while in a fit of rage. This indicates the power he exercises over himself and his ability to overpower the devil.
Source: HadeethEnc.com