Sahih Muslim Book 45, Hadith 139
This hadith has been narrated on the authority of A'mash with the same chain of transmitters.
Whom do you count as" Raqub" amongst you? They (his Companions) said: One who has no children (the children are born unto him but they do not survive). Thereupon he (the Holy Prophet) said: He is not a Raqub but Raqub is one who does not find his child as the forerunner (in Paradise). He then said: Whom do you count as a wrestler amongst you? We said: He who wrestles with persons. He said: No, it is not he but one who controls himself when in a fit of rage.
The strong-man is not one who wrestles well but the strong man is one who controls himself when he is in a fit of rage.