Musnad Ahmad 30:101

'Abd al-Rahman narrated to us, Malik narrated to us, from al-Zuhri, from Sa'id ibn al-Musayyib, from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, who said: "The strong one is not the one who overcomes people in wrestling; rather, the strong one is the one who controls himself at the time of anger."