In the words of Sri Sankaracarya, in his book Vivekacudamani (The Crest-Jewel of Discrimination), translated by Swami Turiyananda:

(6) "Men may recite the scriptures and sacrifice to the holly spirits, they may perform rituals and worship deities -- but, until a man wakes to knowledge of his identity with the Atman, liberation can never be obtained; no, not even at the end of many hundreds of Brahma's years."

(7) "The scriptures declare that immortality cannot be gained through work or progeny or riches, but by renunciation alone. Hence it is clear that work cannot bring liberation."

(8) "Therefore, let the wise man give up craving for pleasure in external things, and struggle hard for liberation. …"

(9) "Through devotion to right discrimination he will climb to the height of union with Brahman. By the power of Atman, let him rescue his own soul which lies drowned in the vast waters of worldliness."

(10) "Let the wise, who have grown tranquil and who practices contemplation of the Atman, give up all worldly activities and struggle to cut the bonds of worldliness."

(11) "Right action helps to purify the heart, but it does not give us direct perception of the Reality. The Reality is attained through discrimination, but not in the smallest degree even by ten million acts."

(14) "Success in attaining the goal depends chiefly upon the qualifications of the seeker. Suitable time, place, and other such circumstances are aids to its attainment."

(21) "Renunciation is the giving up of all the pleasures of the eyes, the ears, and the other senses, the giving up of all objects of transitory enjoyments, the giving up of the desire for a physical body as well as for the highest kind of spirit-body of a god.

(27) "Longing for liberation is the will to be free from the fetters of ignorance -- beginning with the ego-sense and so on, down to the physical body itself -- through realization of one's true nature."

(31) "Among all means of liberation, devotion is supreme. To seek earnestly to know one's real nature -- this is said to be devotion."

(51) "Children may free their father from his debts, but no other person can free a man from his bondage; he must do it himself."

(54) "A clear vision of the Reality may be obtained only through our own eyes, when they have been opened by spiritual insight -- never through the eyes of some other seer. Through our own eyes we learn what the moon looks like; how could we learn this through the eyes of others?"

(55) "Those cords that bind us, because of our ignorance, our lustful desires and the fruits of our Karma -- how could anybody but ourselves untie them, even in the course of innumerable ages?"

(56) "Neither by the practice of Yoga or of Sankhya philosophy, nor by good works, nor by learning, does liberation come; but only through the realization that Atman and Brahman are one -- in no other way."

(59) "Study of the scriptures is fruitless as long as Brahman has not been experienced. And when Brahman has been experienced, it is useless to read the scriptures."

(62) "A sickness is not cured by saying the word "medicine". You must take the medicine. Liberation does not come by merely saying the word "Brahman". Brahman must be actually experienced."

(63) "Until you allow this apparent universe to dissolve from your consciousness -- until you have experienced Brahman -- how can you find liberation just by saying the word "Brahman"? The result is merely noise."

(80) "One who tries to cross this ocean meets the great crocodile of desire, and must kill that by the sword of non-attachment."

(82) "If you have desire for liberation, give up like poison from a long distance the objects of senses; and take to contentment, kindness, forgiveness, straightforwardness and peace."

(110) "… Knowledge of Brahman -- the One, pure, without a second -- destroys it (Maya), as the illusion of the snake in the rope is destroyed when the nature of the rope is known."

(142) "As the sun creates the cloud, and then the cloud hides the sun; so egotism takes rise from the Atman (and then veils it)."

(172) "As the wind creates the clouds and again destroys them, so this bondage is the creation if the mind, and it is the mind also that destroys that bondage."

(182) "I tell you this: Have desire for liberation alone, not for anything else. Be resolute for liberation. …"

(196) "The seer, beyond all qualities, all actions -- the blissful Atman -- has taken this state of being "I" through ignorance only. It is not real. When ignorance comes to naught, it does not remain."

(223) "This is the cause of liberation from the world -- the consciousness, the knowledge of the non-separateness of the self from the Supreme. By this knowledge, one attains that Bliss Eternal."

(235) "What appears cannot be real. The basis is the real thing, and the appearance is only through ignorance."

(237) "Therefore, the Supreme Soul is alone real -- One without a second, pure consciousness, without any blemish, quiet, beginning-less, endless, beyond all actions, always Blissfulness Itself."

-----------

From the Yoga Sutras by Patanjali, translated by Swami Prabhavananda and Christopher Isherwood (titled "How to Know God -- the Yoga Aphorisms of Patanjali"):

(I 16) "When through the knowledge of the Atman, one ceases to desire any manifestation of Nature, then that is the highest kind of non-attachment."

(I 49) "The knowledge which is gained from inference and the study of the scriptures is knowledge of one kind. But the knowledge which is gained from samadhi is of much higher order. It goes beyond inference and scriptures."

(II 5) "To regard the non-eternal as eternal, the impure as pure, the painful as pleasant and the non-Atman as the Atman -- this is ignorance."

(II 6) "To identify consciousness with that which merely reflects consciousness -- this is egoism."

(II 16) "The pain which is yet to come may be avoided."

(II 17) "This pain is caused by false identification of the experiencer with the object of experience. It may be avoided."

(II 20) "The Atman -- the experiencer -- is pure consciousness. It appears to take the changing colors of the mind. In reality, it is unchangeable."

(II 28) "As soon as all impurities have been removed by the practice of the spiritual disciplines -- the "limbs" of yoga -- a man's spiritual vision opens to the light-giving knowledge of Atman."

(II 29) "The eight limbs of yoga are: the various forms of abstention from evil-doing (yama), the various observances (niyamas), posture (asana), control of prana (pranayama), withdrawal of the mind from sense objects (pratyahara), concentration (dharana), meditation (dhyana) and absorption in the Atman (samadhi)."