Who kindly sets a wand’rer on his way
Does e’en as if he lit another’s lamp by his:
No less shines his, when he his friend’s hath lit.

[Homó, qui erranti cómiter monstrát viam,
Quasi lúmen de suo lúmine accendát, facit.
Nihiló minus ipsi lúcet, cum illi accénderit.]

Quintus Ennius (239-169 BC) Roman poet, writer
Telephus, frag 412-414 [tr. Miller (1913)]
    (Source)

The fragment comes to us from Cicero, De Officiis [On Duties; On Moral Duty; The Offices], Book 1, ch. 16 / sec. 51 (44 BC). Original Latin. Alt. trans.:

He that directs the wandering traveller,
Doth, as it were, light another's torch by his own;
Which gives him ne'er the less of light, for that
It gave another.
[tr. Cockman (1699)]

The man who kindly points out the way to the wandering traveller, gives light to the lamp of another, without diminishing by the communication the light of his own.
[tr. McCartney (1798)]

He who kindly shows the bewildered traveller the right road, does as it were light his lamp by his own; which affords none the less light to himself after it has lighted the other.
[tr. Edmonds (1865)]

Who kindly shows a wanderer his way,
Lights, as it were, a torch from his own torch, --
In kindling others' light, no less he shines.
[tr. Peabody (1883)]

The man who kindly points the way top a wanderer, does as though he kindles a light from the light that is his; it shines none the less for himself when he has kindled it for his fellow.
["trib Teleph. R suae lumine accendit facis Hartman, Mnemoe., XXI, 382 fortass recte"]