Quotations about:
    discretion

To go on with my advice (that is, supposing
You need advice from me): Be careful about
The things you say and the people to whom you say them.
Avoid the man who asks too many questions.
No question but he’ll be a teller of tales;
An ear that eager can’t keep a secret for long,
And once a word slips out it won’t come back.

[Protinus ut moneam (si quid monitoris eges tu)
quid de quoque viro et cui dicas, saepe videto,
percontatorem fugito: nam garrulus idem est,
nec retinent patulae commissa fideliter aures,
et semel emissum volat irrevocabile verbum.]

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

Epistles [Epistularum, Letters], Book 1, ep. 18 “To Lollius,” l. 67ff (1.18.67-71) (20 BC) [tr. Ferry (2001)]
    (Source)

(Source (Latin)). Other translations:

Further for to admonishe the (If therof thou standst neede)
What, of what men, to whom thou speakest, take ever earnest heede.
A groper after novelties, in any wise do flye.
I warrante the learne this of me the same's a verye pye.
Nor wyde ope eares the thinges of trust can well conceale at all,
And word once scaped, away its gone, and none can it recall.
[tr. Drant (1567)]

When thou dost talk of any man, take care
Of whom, to whom, and what thy speeches are.
Shun him that is inquisitive, for he
Will be as guilty of Garrulitie.
And his still gaping ears itch to reveal
What e're his friend intrusts him to conceal.
And 'tis impossible e're to recall
One syllable which we have once let fall.
[tr. A. B.; ed. Brome (1666)]

But to advise you, if you want advice,
Take heed of whom you speak, and what it is,
Take heed to whom, avoid the busy Men,
Fly the inquisitive, they'l talk agen,
And tell what you have said, a leaky Ear
Can never hold what it shall chance to hear,
'Twill run all out, and what you once let fall
It flys, and tis impossible to recall.
[tr. Creech (1684)]

If my advice regard my claim,
Be tender of another's fame,
And be the man with caution tried.
In whose discretion you confide.
The impertinent be sure to hate;
Who loves to ask, will love to prate.
Ears, that unfold to every tale,
Entrusted secrets ill conceal,
And you shall wish, but wish in vain,
To call the fleeting words again.
[tr. Francis (1747)]

But with our sage monitions to proceed,
If peradventure such advice you need --
When of men's characters you speak, beware
Of whom, to whom, and what those speeches are!
Shun the inquisitive: pert fools will prate;
And words once utter'd are recall'd too late.
[tr. Howes (1845)]

Moreover, that I may advise you (if in aught you stand in need of an adviser), take great circumspection what you say to any man, and to whom. Avoid an inquisitive impertinent, for such a one is also a tattler, nor do open ears faithfully retain what is intrusted to them; and a word, once sent abroad, flies irrevocably.
[tr. Smart/Buckley (1853)]

Well, to proceed; beware, if there is room
For warning, what you mention, and to whom;
Avoid a ceaseless questioner; he burns
To tell the next he talks with what he learns;
Wide ears retain no secrets, and you know
You can't get back a word you once let go.
[tr. Conington (1874)]

But with my words of warning to proceed.
If haply you a word of warning need!
Ere of a man you tell a thing, think well
To whom you tell it, also what you tell.
The man that pesters you with questions shun --
Tattlers are dangerous, and he is one.
Wide-gaping ears no secrets can retain.
And words once spoken you woo back in vain.
[tr. Martin (1881)]

Further let me advise you, if you need advice, to be careful what you say about anybody and to whom you say it. Avoid a gossip. He is always a tattler; his widespread ears do not keep the secrets committed to them, and a word once spoken never returns.
[tr. Dana/Dana (1911)]

To continue my advice, if you need advice in aught — think often of what you say, and of whom, and to whom you say it. Avoid a questioner, for he is also a tattler. Open ears will not keep secrets loyally, and the word once let slip flies beyond recall.
[tr. Fairclough (Loeb) (1926)]

If my advice regard may claim,
Be tender of another's fame,
And be the man with caution tried
In whose discretion you confide.
Th' impertinent be sure to hate;
Who loves to ask, will love to prate.
Ears, that unfold to every tale,
Intrusted secrets ill conceal,
And you shall wish, but wish in vain,
To call the fleeting words again.
[tr. Murison (1931); ed. Kramer, Jr. (1936)]

Let me give you some more advice -- not that you need it.
Becareful of what you say and to whom and of whom.
Steer clear of inquisitive snoopers: they're usually gossips.
Open ears will nto keep safe what's deposited in them,
And a word once launched on its way cannot be revoked.
[tr. Palmer Bovie (1959)]

In case you need some more advice, I offer this:
Be careful what you say and to whom, and about whom.
Run from a curious man; he'll love telling others.
Secrets that you trust to open ears won't be well kept,
and once a word escapes, it flies; you can't recall it.
[tr. Fuchs (1977)]

Another word of advice -- if in fact you need an adviser:
watch what you say, and of which man, and to whom you say it.
Have nothing to do with inquisitive people -- they're also gossips.
You cannot rely on ready ears to contain a secret,
And once a word escapes, it flies beyond recall.
[tr. Rudd (2005 ed.)]

On with the advice (if you need any advice):
Always think what you say to whom, and of whom.
Avoid the inquisitive: they’re also garrulous,
Flapping ears can’t be trusted to keep a secret,
And once the word’s let slip, it flies beyond recall.
[tr. Kline (2015)]