Not to commit any sin, to do good, and to purify one's mind, that is the teaching of (all) the Awakened.
Sabbapāpassa akaraṇaṁ, kusalassa upasampadā; Sacittapariyodapanaṁ, etaṁ buddhāna sāsanaṁ.
Dhammapada 183
The same idea in other traditions
Keep thy tongue from evil, And thy lips from speaking guile.
A soft answer turneth away wrath: but grievous words stir up anger.
The Master said, "The superior man wishes to be slow in his speech and earnest in his conduct."
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,-
Be silent, O thou who knowest many things! for he that speaketh little will be free from reproach on the Day of Judgment. The man of many words is deaf; no counsel does he heed like silence. …
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.
(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.