ब्राह्मण उवाच

सत्त्वस्य रजसश्चैव तमसश्च यथातथम् | गुणांस्तत्त्वेन मे ब्रूहि यथावदिह पृच्छतः ||
ब्राह्मण asked: Truly described to me as I ask you to convey the respective specifics about सत्व, रजस् and तमस् गुण.  

व्याध उवाच
हन्त ते कथयिष्यामि यन्मां त्वं परिपृच्छसि | एषां गुणान्पृथक्त्वेन निबोध गदतो मम ||
व्याध said: I shall tell you what you ask of me. I shall separately describe to you their respective details. Listen to them. 

मोहात्मकं तमस्तेषां रज एषां प्रवर्तकम् | प्रकाशबहुलत्वाच्च सत्त्वं ज्याय इहोच्यते ||
तमस् is characterized by मोह (obsessive attachment or infactuation triggered by absence of knowledge), रजस् incites persons to कर्म (or action) while सत्व is characterized by light and is therefore called the greatest of all.

अविद्याबहुलो मूढः स्वप्नशीलो विचेतनः | दुर्दृशीकस्तमोध्वस्तः सक्रोधस्तामसोऽलसः ||
He who is greatly under the influence of अविद्या (ignorance of आध्यात्म), who is मूढः (foolish), senseless and given to day-dreaming, who is idle, unenergetic, full to anger and pride is said to be under the influence of तमस्. 

प्रवृत्तवाक्यो मन्त्री च योऽनुराग्यभ्यसूयकः | विवित्समानो विप्रर्षे स्तब्धो मानी स राजसः ||
That excellent man who is agreeable in speech, thoughtful, free from envy, industrious in action from an eager desire to reap the fruits (of action) and of warm temperament is said to be under the influence of रजस्

प्रकाशबहुलो धीरो निर्विवित्सोऽनसूयकः | अक्रोधनो नरो धीमान्दान्तश्चैव स सात्त्विकः ||
He who is firm (in धर्म), patient, not subject to anger, free from jealousy and who does not undertake actions to satisfy selfish desire of reaping fruits of the action, who is wise and forgiving is said to be under the influence of सत्व. 

सात्त्विकस्त्वथ संबुद्धो लोकवृत्तेन क्लिश्यते | यदा बुध्यति बोद्धव्यं लोकवृत्तं जुगुप्सते ||
वैराग्यस्य हि रूपं तु पूर्वमेव प्रवर्तते | मृदुर्भवत्यहंकारः प्रसीदत्यार्जवं च यत् ||
ततोऽस्य सर्वद्वंद्वानि प्रशाम्यन्ति परस्परम् | न चास्य संयमो नाम क्वचिद्भवति कश्चन ||
When a person endued with सत्व गुण is influenced by लौकिक orientation, he suffers misery and he starts hating his लौकिक orientation once he realizes its full significance. Then a feeling of indifference to worldly affairs begins to influence him. And then his pride decreases and yearning for simplicity (or upright conduct) becomes more prominent. His conflicting sentiments are reconciled (he becomes balanced) and any (forced) self-restraint becomes unnecessary for such a person. 

शूद्रयोनौ हि जातस्य सद्गुणानुपतिष्ठतः | वैश्यत्वं भवति ब्रह्मन्क्षत्रियत्वं तथैव च ||
आर्जवे वर्तमानस्य ब्राह्मण्यमभिजायते | गुणास्ते कीर्तिताः सर्वे किं भूयः श्रोतुमिच्छसि ||
O ब्राह्मण! A man may be born as a शूद्र but if he is endued with सद्गुण, he may attain the state of वैश्य or of a kshatriya or even a ब्राह्मण if he is steadfast in goodness/ character. I have described all three गुण to you – tell me what else would you want to hear. 

Source:

Translation of Mahabharata by MN Dutt