While then the worst man is he who displays vice both in his own affairs and in his dealings with his friends, the best man is not he who displays virtue in his own affairs merely, but he who displays virtue towards others; for this is the hard thing to do.

[κάκιστος μὲν οὖν ὁ καὶ πρὸς αὑτὸν καὶ πρὸς τοὺς φίλους χρώμενος τῇ μοχθηρίᾳ, ἄριστος δ᾽ οὐχ ὁ πρὸς αὑτὸν τῇ ἀρετῇ ἀλλὰ πρὸς ἕτερον: τοῦτο γὰρ ἔργον χαλεπόν.]

Aristotle (384-322 BC) Greek philosopher

Nicomachean Ethics [Ἠθικὰ Νικομάχεια], Book 5, ch. 1 (5.1.18) / 1130a.5-8 (c. 325 BC) [tr. Peters (1893)]
    (Source)

(Source (Greek)). Alternate translations:

Now he is the basest of men who practises vice not only in his own person, but towards his friends also; but he the best who practises virtue not merely in his own person but towards his neighbour, for this is a matter of some difficulty.
tr. Chase (1847), ch. 2]

Worst of men is he whose wickedness affects not himself alone but his fellow with him; best of men is he whose virtue affects not himself alone but his fellow with him; for such a one has in all sooth a hard task.
[tr. Williams (1869)]

As then the worst of men is he who exhibits his depravity both in his own life and in relation to his friends, the best of men is he who exhibits his virtue not in his own life only but in relation to others; for this is a difficult task.
[tr. Welldon (1892)]

Now the worst man is he who exercises his wickedness both towards himself and towards his friends, and the best man is not he who exercises his virtue towards himself but he who exercises it towards another; for this is a difficult task.
[tr. Ross (1908)]

As then the worst man is he who practises vice towards his friends as well as in regard to himself, so the best is not he who practises virtue in regard to himself but he who practises it towards others; for that is a difficult task.
[tr. Rackham (1934)]

The worst sort of person, then, is the one who uses his depravity both in relation to himself and in relation to his friends, whereas the best sort is not the one who uses his virtue in relationship to himself but the one who uses it in relation to another person, since that is difficult work.
[tr. Reeve (1948)]

The worst man, then, is the one whose evil habit affects both himself and his friends, while the best man is one whose virtue is directed not to himself, but to others, for this is a difficult task.
[tr. Apostle (1975)]

So the worst person is the one who exercises his wickedness towards both himself and his friends, and the best is not the one who exercises his virtue towards himself but the one who exercises it towards another; because this is a difficult task.
[tr. Thomson/Tredennick (1976)]

So the worst person is the one who exercises wickedness in relation to himself and in relation to his friends, and the best is not he who exercises his virtue in relation to himself but the one who exercises it in relation to others, since this is a difficult thing to do.
[tr. Crisp (2000)]

Worst, then, is he who treats both himself and his friends in a corrupt way, but best is he who makes use of virtue not in relation to himself but in relation to another. For this is a difficult task.
[tr. Bartlett/Collins (2011)]