When you see someone who is worthy, concentrate upon becoming their equal; when you see someone who is unworthy, use this as an opportunity to look within yourself.

[見賢思齊焉、見不賢而內自省也。]

Confucius (c. 551- c. 479 BC) Chinese philosopher, sage, politician [孔夫子 (Kǒng Fūzǐ, K'ung Fu-tzu, K'ung Fu Tse), 孔子 (Kǒngzǐ, Chungni), 孔丘 (Kǒng Qiū, K'ung Ch'iu)]

The Analects [論語, 论语, Lúnyǔ], Book 4, verse 17 (4.17) (6th C. BC – AD 3rd C.) [tr. Slingerland (2003)]
    (Source)

(Source (Chinese)). Alternate translations:

When we see men of worth, we should think of equaling them; when we see men of a contrary character, we should turn inwards and examine ourselves.
[tr. Legge (1861)]

When you meet with men of worth, think how you may attain to their level; when you see others of an opposite character, examine yourself.
[tr. Jennings (1895)]

When we meet with men of worth, we should think how we may equal them. When we meet with worthless men, we should turn into ourselves and find out if we do not resemble them.
[tr. Ku Hung-Ming (1898)]

When you see a man of worth, think how to rise to his level. When you see an unworthy man, then look within and examine yourself.
[tr. Soothill (1910)]

See solid talent and think of measuring up to it; see the un-solid and examine your own insides.
[tr. Pound (1933)]

In the presence of a good man, think all the time how you may learn to equal him. In the presence of a bad man, turn your gaze within!
[tr. Waley (1938)]

When you see a man of the highest caliber, give thought to attaining his stature. When you see one who is not, go home and conduct a self-examination.
[tr. Ware (1950)]

When you meet someone better than yourself, turn your thoughts to becoming his equal. When you meet someone not as good as you are, look within and examine your own self.
[tr. Lau (1979)]

When you come across a superior person, think of being equal to him. When you come across an inferior person, turn inwards and examine yourself.
[tr. Dawson (1993)]

When you see a worthy man, seek to emulate him. When you see an unworthy man, examine yourself.
[tr. Leys (1997)]

On seeing a worthy man, think of equalling him; on seeing an unworthy man, examine yourself inwardly.
[tr. Huang (1997)]

One should think to follow the sagaciousness when one sees it; One should examine onceself when one sees the no sagaciousness.
[tr. Cai/Yu (1998), #83]

When you meet persons of exceptional character think to stand shoulder to shoulder with them; meeting persons of little character, look inward and examine yourself.
[tr. Ames/Rosemont (1998)]

When he sees a worthy man, let him think how he might come up to him; when he sees an unworthy man, let him examine within himself.
[tr. Brooks/Brooks (1998)]

In the presence of sages, you can see how to perfect your thoughts. In the presence of folls, you must awaken yourself.
[tr. Hinton (1998)]

When you see a worthy person, think about how you can equal him. When you see an unworthy person, reflect on your own conduct.
[tr. Watson (2007)]

When you meet a worthy person, think how you could become his equal. When you meet an unworthy person, turn inward and examine your own conduct.
[tr. Chin (2014)]

When you meet a virtuous person, you should strive to emulate his virtues. When you meet a person void of virtue, you should consider whether you have the same flaws.
[tr. Li (2020)]