Mahabharata Bhishma Parva Chapter 42:3

Mahabharata Bhishma Parva (Bhagavat-Gita Parva) Chapter 42:3
Bhagavad Gita Chapter XVIII

That which is from the contact of the senses with their objects which resembleth nectar first but is like poison in the end, that happiness is held to be of the quality of passion. That happiness which in the beginning and its consequences deludeth the soul, and springeth from sleep, indolence, and stupidity, that is described to be of the quality of darkness. There is not, either on earth or heaven among the gods, the entity that is free from these three qualities born of nature. The duties of Brahmanas, Kshatriyas, and Vaisyas, and of Sudras also, O chastiser of foes, are distinguished by (these three) qualities born of nature. Tranquillity, self-restraint, ascetic austerities, purity, forgiveness, rectitude, knowledge, experience, and belief (in an existence hereafter),—these are the duties of Brahmanas, born of (their proper) nature. Bravery, energy, firmness, skill, not flying away from battle, liberality, the bearing of a ruler,—these are the duties of Kshatriyas, born of (their proper) nature. Agriculture, tending of cattle, and trade, are the natural duties of Vaisyas. Of Sudras also, the natural duty consists in servitude. Every man, engaged in his own duties, attains to perfection. Hear now how one obtains perfection by application to his duties. Him from whom are the movements of all beings, Him by whom all this is pervaded, worshipping him by (the performance of) one's own duty, one obtaineth perfection. Better is one's own duty though performed faultily than another's duty well-performed. Performing the duty prescribed by (one's own) nature, one incurreth no sin. One must not abandon, O son of Kunti, one's natural duty though tainted with evil, for all actions are enveloped by evil like fire by smoke. He whose mind is unattached everywhere, who hath subdued his self, and whose desire hath departed, obtaineth, through renunciation, the supreme perfection of freedom from work. Learn from me, only in brief, O son of Kunti, how one, having obtained (this kind of) perfection, attaineth to Brahma which is the supreme end of knowledge. Endued with a pure mind, and restraining his self by constancy, renouncing sound and other objects of sense, and casting off affection and aversion, he who resideth in a lonely place, eateth little, and restraineth speech, body, and mind, who is ever intent on meditation and abstraction, who hath recourse to indifference, who, abandoning egoism, violence, pride, lust, wrath, and (all) surroundings, hath been freed from selfishness and is tranquil (in mind), becometh fit for assimilation with Brahma. Becoming one with Brahma, tranquil in spirit, (such a) one grieveth not, desireth not; alike to all beings, he obtaineth the highest devotion to Me. By (that) devotion he truly understandeth Me. What I am, and who I am; then understanding Me truly, he entereth into Me forthwith. Even performing all actions at all times having refuge in Me, he obtaineth, through my favour, the seat that is eternal and imperishable. Dedicating in thy heart all actions to Me, being devoted to Me, resorting to mental abstraction, fix thy thoughts constantly on Me.