If one man conquer in battle a thousand times thousand men, and if another conquer himself, he is the greatest of conquerors.
Yo sahassaṁ sahassena, saṅgāme mānuse jine; Ekañca jeyyamattānaṁ, sa ve saṅgāmajuttamo.
Dhammapada 103
The same idea in other traditions
Be not hasty in thy spirit to be angry: for anger resteth in the bosom of fools.
He used to say, If I am not for myself who is for me? and being for my own self what am I? If not now when?
See the brotherhood of all mankind as the highest order of Yogis; conquer your own mind, and conquer the world.
O ye who believe! Fasting is prescribed to you as it was prescribed to those before you, that ye may (learn) self-restraint,-
… From the Son of Heaven down to the mass of the people, all must consider the cultivation of the person the root of everything besides. …
By watchfulness of the mind he concentrates his thoughts; thereby he truly practises control. By watchfulness of speech he keeps free from prevarication; thereby he enables his mind to act properly.
Eat in proportion to thy hunger; how can he give praises who scarce can breathe by reason of his gluttony? He whose stomach is full is void of wisdom. The prey is entrapped in the snare because of its greed. …
(A man) should elevate his self by his self; he should not debase his self, for even (a man's) own self is his friend, (a man's) own self is also his enemy. To him who has subjugated his self by his self, his self is a friend; but to him who has not restrained his self, his own self behaves inimically, like an enemy.