For who could see the passage of a goddess
Unless she wished his mortal eyes aware?

[τίς ἂν θεὸν οὐκ ἐθέλοντα
ὀφθαλμοῖσιν ἴδοιτ᾽ ἢ ἔνθ᾽ ἢ ἔνθα κιόντα]

Homer (fl. 7th-8th C. BC) Greek author
The Odyssey [Ὀδύσσεια], Book 10, l. 575ff (10.575-576) [Odysseus] (c. 700 BC) [tr. Fitzgerald (1961)]
    (Source)

On Circe providing, unseen, a ram and ewe for sacrifice, tied to Odyseus' departing ship.

(Source (Greek)). Alternate translations:

For who would see God, loth to let us see,
This way or that bent; still his ways are free.
[tr. Chapman (1616)]

For Gods, but when they list, cannot be spied.
[tr. Hobbes (1675)]

The paths of gods what mortal can survey?
Who eyes their motion? who shall trace their way?
[tr. Pope (1725)]

For who hath eyes that can discern a God
Going or coming, if he shun the view?
[tr. Cowper (1792)]

For who with eyes may know
Against their will immortals moving to and fro?
[tr. Worsley (1861), st. 65]

Who could see a god
With his own eyes, if he should not be willing, --
Whether he hied him here, or hied him there?
[tr. Bigge-Wither (1869)]

Who may behold a god against his will, whether going to or fro?
[tr. Butcher/Lang (1879)]

For what man's eyes may see
A God that is loth to be looked on, whether here or there he be?
[tr. Morris (1887)]
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When a god does not will, what man can spy him moving to and fro?
[tr. Palmer (1891)]

For who can see the comings and goings of a god, if the god does not wish to be seen?
[tr. Butler (1898), rev. Power/Nagy (1900)]

Who with his eyes could behold a god against his will, whether going to or fro?
[tr. Murray (1919)]

What mortal eye can see a God going up and down if He wills not to be seen?
[tr. Lawrence (1932)]

And when a god wishes to remain unseen, what eye can observe his coming or his going?
[tr. Rieu (1946)]

Whose eyes can follow the movement
of a god passing from place to place, unless the god wishes?
[tr. Lattimore (1965)]

How can
a man detect a god who comes and goes
if gods refuse to have their movements known?
[tr. Mandelbaum (1990)]

Who can glimpse a god
who wants to be invisible gliding here and there?
[tr. Fagles (1996)]

When a god wishes to remain unseen, what eye can observe his coming of going?
[tr. DCH Rieu (2002)]

For when a god does not wish to be observed who can cast an eye upon his going back and forth?
[tr. Verity (2016)]

Who can see the gods go by unless they wish to show themselves to us?
[tr. Wilson (2017)]

When the gods don't desire it, who can witness their passage, either coming or going?
[tr. Green (2018)]

For who can see a god move back and forth,
if she has no desire to be observed?
[tr. Johnston (2019)]