Mahabharata Santi Parva Chapter 247:2

Mahabharata Santi Parva (Mokshadharma Parva) Chapter 247:2 In man there are five senses. The mind is called the sixth (sense). The Understanding is called the seventh. The Soul is the eighth. The eyes (and the other senses) are for only receiving impressions of form (and scent, etc.). The mind exists for doubting (the accuracy of those impressions). The Understanding settles those doubts. The Soul is said only to witness every operation without mingling with them. Rajas, Tamas, and Sattwa,—these three,—arise from their own counterparts. These exist equal in all creatures (viz., the deities and human beings, etc.). These are called attributes and should be known by the actions they induce. As regards those actions all such states in which one becomes conscious of oneself as united with cheerfulness or joy and which are tranquil and pure, should be known as due to the attribute of Sattwa. All such states in either the body or the mind, as are united with sorrow, should be regarded as due to the influence of the attribute called Rajas. All such states again as exist with stupefication (of the senses, the mind or the understanding) whose cause is unascertainable, and which are incomprehensible (by either reasons or inward light), should be known as ascribable to the action of Tamas. Delight, cheerfulness, joy, equanimity, contentment of heart, due to any known cause or arising otherwise, are all effects of the attribute of Sattwa. Pride, untruthfulness of speech, cupidity, stupefication, vindictiveness, whether arising from any known cause or otherwise, are indications of the quality of Rajas. Stupefaction of judgment, heedlessness, sleep, lethargy, and indolence, from whatever cause these may arise, are to be known as indications of the quality of Tamas.'