Anger’s a short frenzy, curb thy Soul,
And check thy rage, which must be rul’d or rule:
Use all thy Art, with all thy force restrain,
And take the strongest Bit, and firmest Rein.

[Ira furor brevis est: animum rege; qui nisi paret
imperat; hunc frenis, hunc tu compesce catena.]

Horace (65–8 BC) Roman poet, satirist, soldier, politician [Quintus Horatius Flaccus]

Epistles [Epistularum, Letters], Book 1, ep. 2 “To Lollius,” l. 62ff (1.2.62) (20 BC) [tr. Creech (1684)]
    (Source)

(Source (Latin)). Other translations:

Ire is shorte wrathe, rule thow thy moode, if it do not obey,
It rules forthwith, it thou with bitte, it thou with chaine must stay.
[tr. Drant (1567)]

Anger id a short madness: Rule thy mind:
Which reigns, if it obeys not: [...]
With chaines, restrain it with an Iron bit.
[tr. Fanshawe; ed. Brome (1666)]

Anger's a shorter phrensie. Passion reigns
If't be n't enslav'd, but curb it in with chains.
[tr. "Dr. W."; ed. Brome (1666)]

Anger's a shorter madness of the mind;
Subdue the tyrant, and in fetters bind.
[tr. Francis (1747)]

'Tis a short madness: calm the rising fit;
Curb it betimes, and tame it to your bit.
[tr. Howes (1845)]

Rage is a short madness. Rule your passion, which commands, if it do not obey; do you restrain it with a bridle, and with fetters.
[tr. Smart/Buckley (1853)]

Wrath is a short-lived madness: curb and bit
Your mind: 'twill rule you, if you rule not it.
[tr. Conington (1874)]

Anger is but a short-lived frenzy-fit.
Your passion then with rein and bit subdue;
If you don't master it, 'twill master you.
[tr. Martin (1881)]

Anger is a passing madness. Be master of your passions which, unless they obey you, command yuou. Control them by rein and cub.
[tr. Elgood (1893)]

Anger is short-lived madness. Rule your passion, for unless it obeys, it gives commands. Check it with bridle -- check it, I pray you, with chains.
[tr. Fairclough (Loeb) (1926)]

Rule your desires:
If they don't obey, they'll command. Bridle them. Chain them!
[tr. Palmer Bovie (1959)]

Anger, no matter how brief, is madness. Rule your passions
or they'll rule you; manage them with reins or with a leash.
[tr. Fuchs (1977)]

Anger is a transient insanity: check your passion or your passion
Checkmates you. Rule it like an unruly horse -- chain it, if you must.
[tr. Raffel (1983)]

A fit of rage
Is a fit of genuine honest-to-goodness madness.
Keep control of your passions. If you don't,
Your passions are sure to get control of you.
Keep control of them, bridle them, keep them in chains.
[tr. Ferry (2001)]

Rage is a burst of madness. Restrain your temper: unless it
obeys it will rule you. Keep it in check with bridle and chain.
[tr. Rudd (2005 ed.)]

Anger’s a brief madness: rule your heart, that unless
It obeys, controls: and check it with bridle and chain.
[tr. Kline (2015)]