Firm faith in the blissful narration of My pastimes, constant chanting of My glories, unwavering attachment to ceremonial worship of Me, praising Me through beautiful hymns, great respect for My devotional service, offering obeisances with the entire body, performing first-class worship of My devotees, consciousness of Me in all living entities, offering of ordinary, bodily activities in My devotional service, use of words to describe My qualities, offering the mind to Me, rejection of all material desires, giving up wealth for My devotional service, renouncing material sense gratification and happiness, and performing all desirable activities such as charity, sacrifice, chanting, vows and austerities with the purpose of achieving Me—these constitute actual religious principles, by which those human beings who have actually surrendered themselves to Me automatically develop love for Me. What other purpose or goal could remain for My devotee?
(Srimad Bhagavatam-----10:19:20-24-----translation).

A poverty-stricken man must automatically undergo austerities and penances because he does not have the wealth to possess anything. Thus his false prestige is vanquished. Always in need of food, shelter and clothing, he must be satisfied with what is obtained by the mercy of providence. Undergoing such compulsory austerities is good for him because this purifies him and completely frees him from false ego.
(Srimad Bhagavatam-----10:10:15-----translation).

A saintly person voluntarily accepts a state of poverty just to become free from material false prestige. Many great kings left their princely standard of living and went to the forest to practice austerity according to Vedic culture, just to become purified. But if one who cannot voluntarily accept such austerity is put into a situation of poverty, he automatically must practice austerity. Austerity is good for everyone because it frees one from material conditions. Therefore, if one is very much proud of his material position, putting him into poverty is the best way to rectify his foolishness. Dāridrya-doṣo guṇa-rāśi-nāśi: when a person is poverty-stricken, naturally his false pride in aristocracy, wealth, education and beauty is smashed. Thus corrected, he is in the right position for liberation.
(Srimad Bhagavatam-----10:10:15-----purport).

On hearing the prayers of Devakī, the Lord replied, “My dear mother, in the millennium of Svāyambhuva Manu, My father Vasudeva was living as one of the Prajāpatis. His name at that time was Sutapā, and you were his wife named Pṛśni. At that time, when Lord Brahmā was desiring to increase the population, he requested you to generate offspring. You controlled your senses and performed severe austerities. By practicing the breathing exercises of the yoga system, both you and your husband could tolerate all the influences of the material laws: the rainy season, the onslaught of the wind, and the scorching heat of the sunshine.
(Krsna Book).

Śukadeva Gosvāmī informed Mahārāja Parīkṣit that for self-realization the austerities and penances performed by the queens at Dvārakā have no comparison. The objective of self-realization is one: Kṛṣṇa. Therefore, although the dealings of the queens with Kṛṣṇa appear just like ordinary dealings between husband and wife, the principal point to be observed is the queens' attachment for Kṛṣṇa. The entire process of austerity and penance is meant to detach one from the material world and enhance one's attachment to Kṛṣṇa, the Supreme Personality of Godhead.
(Krsna Book).

The Supreme Personality of Godhead said: Nonviolence, truthfulness, not coveting or stealing the property of others, detachment, humility, freedom from possessiveness, trust in the principles of religion, celibacy, silence, steadiness, forgiveness and fearlessness are the twelve primary disciplinary principles. Internal cleanliness, external cleanliness, chanting the holy names of the Lord, austerity, sacrifice, faith, hospitality, worship of Me, visiting holy places, acting and desiring only for the supreme interest, satisfaction, and service to the spiritual master are the twelve elements of regular prescribed duties. These twenty-four elements bestow all desired benedictions upon those persons who devotedly cultivate them.
(Srimad Bhagavatam-----11:19:33-35-----translation).

Absorbing the intelligence in Me constitutes mental equilibrium, and complete discipline of the senses is self-control. Tolerance means patiently enduring unhappiness, and steadfastness occurs when one conquers the tongue and genitals. The greatest charity is to give up all aggression toward others, and renunciation of lust is understood to be real austerity. Real heroism is to conquer one's natural tendency to enjoy material life, and reality is seeing the Supreme Personality of Godhead everywhere. Truthfulness means to speak the truth in a pleasing way, as declared by great sages. Cleanliness is detachment in fruitive activities, whereas renunciation is the sannyāsa order of life. The true desirable wealth for human beings is religiousness, and I, the Supreme Personality of Godhead, am sacrifice. Religious remuneration is devotion to the ācārya with the purpose of acquiring spiritual instruction, and the greatest strength is the prāṇāyāma system of breath control.
(Srimad Bhagavatam-----11:19:36-39-----translation).

Real spiritual knowledge is based on the discrimination of spirit from matter, and it is cultivated by scriptural evidence, austerity, direct perception, reception of the Purāṇas' historical narrations, and logical inference. The Absolute Truth, which alone was present before the creation of the universe and which alone will remain after its destruction, is also the time factor and the ultimate cause. Even in the middle stage of this creation's existence, the Absolute Truth alone is the actual reality.
(Srimad Bhagavatam-----11:28:18-----translation).

The Bhagavad-gītā (18.42) describes the brahminical qualities in this way:
śamo damas tapaḥ śaucaṁ kṣāntir ārjavam eva ca
jñānaṁ vijñānam āstikyaṁ brahma-karma svabhāva-jam
"Peacefulness, self-control, austerity, purity, tolerance, honesty, knowledge, wisdom and religiousness—these are the natural qualities by which the brāhmaṇas work."
In the Muktāphala-ṭīkā, it is said:
śamo damas tapaḥ śaucaṁ kṣānty-ārjava-viraktayaḥ
jñāna-vijñāna-santoṣāḥ satyāstikye dvi-ṣaḍ guṇāḥ
"Mental equilibrium, sense control, austerity, cleanliness, tolerance, simplicity, detachment, theoretical and practical knowledge, satisfaction, truthfulness and firm faith in the Vedas are the twelve qualities of a brāhmaṇa."
(Sri Caitanya Caritamrta------2:20:59-----purport).

“"What austerities must the gopīs have performed? With their eyes they always drink the nectar of the form of Lord Kṛṣṇa, which is the essence of loveliness and is not to be equaled or surpassed. That loveliness is the only abode of beauty, fame and opulence. It is self-perfect, ever fresh and unique."
(Sri Caitanya Caritamrta------2:21:112-----translation).

“"Those who perform severe austerities and penances, those who give away all their possessions out of charity, those who are very famous for their auspicious activity, those who are engaged in meditation and mental speculation, and even those who are very expert in reciting the Vedic mantras are not able to obtain any auspicious results, although they are engaged in auspicious activities, if they do not dedicate their activities to the service of the Supreme Personality of Godhead. I therefore repeatedly offer my respectful obeisances unto the Supreme Personality of Godhead, whose glories are always auspicious."
(Sri Caitanya Caritamrta------2:22:20-----translation).

Austerity of the body consists in worship of the Supreme Lord, the brāhmaṇas, the spiritual master, and superiors like the father and mother, and in cleanliness, simplicity, celibacy and nonviolence.
(Bhagavad-Gita-----17:14-----translation).

Austerity of speech consists in speaking words that are truthful, pleasing, beneficial, and not agitating to others, and also in regularly reciting Vedic literature.
(Bhagavad-Gita-----17:15-----translation).

“"The taste for loving service is like the water of the river Ganges, which flows from the feet of Lord Kṛṣṇa. Every day that taste diminishes the results of sinful activities acquired over a period of many births by those who perform austerities."
(Sri Caitanya Caritamrta------2:24:217-----translation).

“Chanting the holy name is the chief means of attaining love of Godhead. This chanting or devotional service does not depend on any paraphernalia, nor on one's having taken birth in a good family. By humility and meekness one attracts the attention of Kṛṣṇa. That is the verdict of all the Vedas. Therefore if one becomes very humble and meek, he can easily attain the lotus feet of Kṛṣṇa in this Age of Kali. That is the fulfillment of all great sacrifices, penances and austerities because when one achieves ecstatic love of Godhead, he attains the complete perfection of life. Therefore whatever one does in executing devotional service must be accompanied by the chanting of the holy name of the Lord.”
(Sri Caitanya Caritamrta------3:4:71-----purport).

Peacefulness, self-control, austerity, purity, tolerance, honesty, knowledge, wisdom and religiousness—these are the natural qualities by which the brāhmaṇas work.
(Bhagavad-Gita-----18:42-----translation).

"O son of Kuntī, all that you do, all that you eat, all that you offer and give away, as well as all austerities that you may perform, should be done as an offering unto Me." With love and affection, one should try to give something to Kṛṣṇa from one's source of income. Then one's life will be successful. Kṛṣṇa is full in all opulences; He does not need anything from anyone. But if one is prepared to give something to Kṛṣṇa, that is for one's own benefit. The example given in this connection is that when one's real face is decorated, the reflection of one's face is automatically decorated. Similarly, if we try to serve Kṛṣṇa with all our opulences, we, as parts and parcels or reflections of Kṛṣṇa, will become happy in exchange. Kṛṣṇa is always happy, for He is ātmārāma, fully satisfied with His own opulence.
(Srimad Bhagavatam-----10:11:11-----purport).

O mother earth, what austerity did you perform to attain the touch of Lord Keśava's lotus feet, which has brought you such great joy that your bodily hairs are standing on end? You appear very beautiful in this condition. Was it during the Lord's current appearance that you acquired this ecstatic symptom, or was it perhaps much earlier, when He stepped upon you in His form of the dwarf Vāmanadeva, or even earlier, when He embraced you in His form of the boar Varāhadeva?
(Sri Caitanya Caritamrta------3:4:71-----translation).

“"Although the nectar of Kṛṣṇa"s lips is the absolute property of the gopīs, the flute, which is just an insignificant stick, is forcibly drinking that nectar and loudly inviting the gopīs to come drink it also. Just imagine the strength of the flute's austerities and good fortune! Even great devotees drink the nectar of Kṛṣṇa's lips after the flute has done so.
(Sri Caitanya Caritamrta------3:16:145-----translation).

To make the mind austere is to detach it from sense gratification. It should be so trained that it can be always thinking of doing good for others. The best training for the mind is gravity in thought. One should not deviate from Kṛṣṇa consciousness and must always avoid sense gratification. To purify one's nature is to become Kṛṣṇa conscious. Satisfaction of the mind can be obtained only by taking the mind away from thoughts of sense enjoyment. The more we think of sense enjoyment, the more the mind becomes dissatisfied. In the present age we unnecessarily engage the mind in so many different ways for sense gratification, and so there is no possibility of the mind's becoming satisfied. The best course is to divert the mind to the Vedic literature, which is full of satisfying stories, as in the Purāṇas and the Mahābhārata. One can take advantage of this knowledge and thus become purified. The mind should be devoid of duplicity, and one should think of the welfare of all. Silence means that one is always thinking of self-realization. The person in Kṛṣṇa consciousness observes perfect silence in this sense. Control of the mind means detaching the mind from sense enjoyment. One should be straightforward in his dealings and thereby purify his existence. All these qualities together constitute austerity in mental activities.

(Bhagavad-Gita-----17:16-----purport).