When you see a worthy man, seek to emulate him. When you see an unworthy man, examine 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 [Lun Yü], 4.17 (6th C. BC) [ed. Lao-Tse; tr. Leys (1997)]
    (Source)

Alt. trans.:

• "When we see men of worth, we should think of equalling them; when we see men of a contrary character, we should turn inwards and examine ourselves." [tr. Legge (1930)]
• "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)]
• "On seeing a worthy man, think of equalling him; on seeing an unworthy man, examine yourself inwardly." [tr. Huang (1997)]
• "When you see a good man, try to emulate his example, and when you see a bad man, search yourself for his faults."